UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

For the fiscal year ended December 31, 20162017

OR

FOR THE TRANSITION PERIOD FROM                      TO                     

Commission File Number 001-36164

Twitter, Inc.

(Exact name of registrant as specified in its charter)

1355 Market Street, Suite 900

San Francisco, California 94103

(Address of principal executive offices and Zip Code)

(415) 222-9670

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    YES  ☒    NO  ☐

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act.    YES  ☐    NO  ☒

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    YES  ☒    NO  ☐

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    YES  ☒    NO   ☐

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.   ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company, or an emerging growth company. See the definitiondefinitions of “large accelerated filer”, “accelerated filer”, and “smaller reporting company”, and “emerging growth company” in Rule 12b-2 of the Exchange Act. (Check one):

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    YES  ☐    NO  ☒

The aggregate market value of the voting and non-voting common equity held by non-affiliates of the registrant, based on the closing price of a share of the registrant’s common stock on June 30, 20162017 as reported by the New York Stock Exchange on such date was approximately $10,883,506,044.$12,055,483,328.  Shares of the registrant’s common stock held by each executive officer, director and holder of 5% or more of the outstanding common stock have been excluded in that such persons may be deemed to be affiliates. This calculation does not reflect a determination that certain persons are affiliates of the registrant for any other purpose.

The number of shares of the registrant’s common stock outstanding as of February 17, 20178, 2018 was 726,894,203.750,904,551.

Portions of the registrant’s Definitive Proxy Statement relating to the Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s fiscal year ended December 31, 2016.2017.

TABLE OF CONTENTS

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, which statements involve substantial risks and uncertainties. Forward-looking statements generally relate to future events or our future financial or operating performance. In some cases, you can identify forward-looking statements because they contain words such as “may,” “will,” “should,” “expects,” “plans,” “anticipates,” “could,” “intends,” “target,” “projects,” “contemplates,” “believes,” “estimates,” “predicts,” “potential” or “continue” or the negative of these words or other similar terms or expressions that concern our expectations, strategy, plans or intentions. Forward-looking statements contained in this Annual Report on Form 10-K include, but are not limited to, statements about:

We caution you that the foregoing list may not contain all of the forward-looking statements made in this Annual Report on Form 10-K.

You should not rely upon forward-looking statements as predictions of future events. We have based the forward-looking statements contained in this Annual Report on Form 10-K primarily on our current expectations and projections about future events and trends that we believe may affect our business, financial condition, operating results, cash flows or prospects. The outcome of the events described in these forward-looking statements is subject to risks, uncertainties and other factors described in the section titled “Risk Factors” and elsewhere in this Annual Report on Form 10-K. Moreover, we operate in a very competitive and rapidly changing environment. New risks and uncertainties emerge from time to time and it is not possible for us to predict all risks and uncertainties that could have an impact on the forward-looking statements contained in this Annual Report on Form 10-K. We cannot assure you that the results, events and circumstances reflected in the forward-looking statements will be achieved or occur, and actual results, events or circumstances could differ materially from those described in the forward-looking statements.

The forward-looking statements made in this Annual Report on Form 10-K relate only to events as of the date on which the statements are made. We undertake no obligation to update any forward-looking statements made in this Annual Report on Form 10-K to reflect events or circumstances after the date of this Annual Report on Form 10-K or to reflect new information or the occurrence of unanticipated events, except as required by law. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements and you should not place undue reliance on our forward-looking statements. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.

NOTE REGARDING KEY METRICS

We review a number of metrics, including monthly active users, or MAUs, changes in daily active users or daily active usage, or DAUs, changes in ad engagements and changes in cost per ad engagement, to evaluate our business, measure our performance, identify trends affecting our business, formulate business plans and make strategic decisions. See the section titled “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Key Metrics” for a discussion of how we calculate MAUs, changes in DAUs, changes in ad engagements and changes in cost per ad engagement.

The numbers of active users presented in this Annual Report on Form 10-K are based on internal company data. While these numbers are based on what we believe to be reasonable estimates for the applicable period of measurement, there are inherent challenges in measuring usage and user engagement across our large user base around the world. Furthermore, our metrics may be impacted by our information quality efforts, which are our overall efforts to reduce malicious activity on the service, inclusive of spam, malicious automation, and fake accounts. For example, there are a number of false or spam accounts in existence on our platform. We have performed an internal review of a sample of accounts and estimate that false or spam accounts represented lessfewer than 5% of our MAUs as of December 31, 2016.2017. In making this determination, we applied significant judgment, so our estimation of false or spam accounts may not accurately represent the actual number of such accounts, and the actual number of false or spam accounts could be higher than we have estimated. We are continually seeking to improve our ability to estimate the total number of spam accounts and eliminate them from the calculation of our active users, and in the past have made improvements in our spam detection capabilities that have resulted in the suspension of a large number of spam, malicious automation and fake accounts and intend to continue to make such improvements. After we determine an account is spam, malicious automation or fake, we stop counting it in our MAU, DAU or related metrics. Additionally, we rely on third-party SMS aggregators and mobile carriers to deliver SMS messages to certain of our users when we send our SMS messages to such accounts. Spam accounts thatIf, however, we have identified are notified of material deliverability issues because of, for example, infrastructure issues at the service-provider level or governmental restrictions based on content, we do not includedinclude the affected users in the active user numbers presented in this Annual Report on Form 10-K. MAUs. We also treat multiple accounts held by a single person or organization as multiple users for purposes of calculating our active users because we permit people and organizations to have more than one account. Additionally, some accounts used by organizations are used by many people within the organization. As such, the calculations of our active users may not accurately reflect the actual number of people or organizations using our platform.

OurCertain metrics are also affected byinclude users that access Twitter through applications that automatically contact our servers for regular updates with no discernible user-initiated action involved, and thisinvolved. This activity can causecauses our system to count the usersMAUs associated with such applications as active users on the day or days such contact occurs. As of December 31, 2016, approximately2017, fewer than 8.5% of usersMAUs used third partythird-party applications that may have automatically contacted our servers for regular updates without any discernible additional user-initiated action.  As such, the calculations of our active users presented in this Annual Report on Form 10-K may be affectedaction, which we refer to as a result of this activity.third-party auto-polling MAU.

In addition, our data regarding user geographic location for purposes of reporting the geographic location of our MAUs is based on the IP address or phone number associated with the account when a user initially registered the account on Twitter. The IP address or phone number may not always accurately reflect a user’s actual location at the time such user engaged with our platform. For example, a mobile user may appear to be accessing Twitter from the location of the proxy server that the user connects to rather than from a user’s actual location.

We regularly review and may adjust our processes for calculating our internal metrics to improve their accuracy. Our measures of user growth and user engagement may differ from estimates published by third parties or from similarly-titled metrics of our competitors due to differences in methodology.

We present and discuss ourOur total audience metrics are based on both internal metrics and relying on data from Google Analytics, which measures logged-out visitors to our properties.

PART I

Item 1. BUSINESS

Overview

Twitter is the best and fastest place to see what iswhat’s happening and what people are talking about all around the world.about. Every day, instances of breaking news, entertainment, sports, politics, big events and everyday interests happen first on Twitter. Twitter is where the full story unfolds with all the live commentary and where live events come to life unlike anywhere else. Our primary service can be accessed on a variety of mobile devices, at twitter.com and via SMS.  

Twitter made significant financial and operational progress in 2017, consistently delivering improved financial performance and double-digit year-over-year growth in DAU throughout the year. Our disciplined execution against our priorities led to steady recovery in revenue and margin improvement as the year progressed, putting us in a stronger position as we head into 2018.

In 2016,2018, we remain focused on positioningmaking Twitter for long-term sustainable growtheasier to use as well as making it easier to Tweet and discover content. We are committed to making progress toward GAAP profitability. Specifically, we clearly identified who we are—the best and fastest place to see what’s happening in the world and what people are talking about.  We built and shipped product features that directly improved our key audience growth and engagement metrics.  We also simplified the organization to be what we believe is more focused and efficient, and eliminated investment in non-core areas of our business, like Vine, which we shut down in early 2017, and Fabric, which we sold in early 2017.  We saw accelerating rates of growth on a year-over-year basis for daily active usage, or DAU, for three quarters in a row. Our advertising business saw increasing competition for advertiser spendingTwitter safer, and we are clarifying our policies, improving our enforcement, and communicating more clearly. We believe that advertisingour revenue growth will continuepriorities are leading to lag that of audience growth.

In 2017, our focus is building and shipping product changes more rapidlyimprovements to make Twitter safer.  We intend to invest in our core use casead offerings through better performance and inmeasurement (including ad platform improvements, self-serve measurement studies, and third-party accreditation); tapping into new channels of demand (such as online video); introducing new ways to buy ads on Twitter; and continuing to grow data and enterprise solutions revenue through our new product areas — such as live streaming video, among others — that further strengthen Twitter’s unique position as the best and fastest place to see and talk about what’s happening in the world. We intend to continue integrating new, dynamic, and personalized content as we recognized the importance of simplifying and creating a single destination for people to discover what’s happening on Twitter.  We also plan to simplify and differentiate our revenue products to drive sustainable long-term revenue growth by working to strengthen our unique value proposition, especially in live and video, that gives advertisers the ability to reach the most engaging audiences in the right context at the right time.  We intend to apply the same focused approach that drove renewed monthly and daily usage growth in 2016 to simplify our portfolio and our buying process for advertisers.channel segmented go-to-market approach.  

Products and Services for Users

Twitter.  Our primary service, Twitter, is a global platform for public self-expression and conversation in real time. Twitter allows people to consume, create, distribute and discover content and has democratized content creation and distribution. The reach of Twitter content is not limited to our logged-in users on the Twitter platform, but rather extends to a larger global audience.

The public nature of the Twitter platform allows us and others to extend the reach of Twitter content beyond our properties. Media outlets and our platform partners distribute Tweets beyond our properties to complement their content by making it more timely, relevant and comprehensive. These outlets and partners also add value to our user experience by contributing content to our platform. Many of the world’s most trusted media outlets, including the BBC, CNN, Bloomberg and the Associated Press, regularly use Twitter as a platform for content distribution.

Periscope.  Periscope is a mobile application that lets anyone broadcast and watch video live with others. Periscope broadcasts can also be viewed through Twitter and on desktop or mobile web browser.  In 2016, we continuedbrowsers. We continue to ship significant product updates, building more of Periscope’s technology intoimplement live broadcasts across Twitter, itself,including trends and creating new, immersive video formats like live 360 video. We also introduced the abilitymoments, to create and Tweet live video from the Twitter app, powered by Periscope. Pairing Periscope with Twitter gives broadcasters greater distribution (anywhere a Tweet can be displayed, a Periscope can be too) and the ability to integrate into our revenue products. We do not currently monetize videos on Periscope, other than to the extent they can be integrated into our revenue products.help people discover what’s happening live.

Products and Services for Advertisers

Our Promoted Products enable our advertisers to promote their brands, products and services, amplify their visibility and reach, and extend the conversation around their advertising campaigns. We enable our advertisers to target an audience based on a variety of factors, including a user’s Interest Graph. The Interest Graph maps, among other things, interests based on users followed and actions taken on our platform, such as Tweets created and engagement with Tweets. We believe a user’s Interest Graph produces a clear and real-time signal of a user’s interests, greatly enhancing the relevance of the ads we can display for users and enhancing our targeting capabilities for advertisers. Our Promoted Products are incorporated into our platform as native advertising and are designed to be as compelling and useful to our users as organic content on our platform.

Currently, our Promoted Products (all of which are labeled “promoted” within Twitter) consist of:

Advertisers can also run short video ads, such as In-Stream video ads, either before (also known as pre-roll ads) or during (also known as mid-roll ads)around premium video content, such as during our live NFL games, live election debate coverageathletic events or clips from a variety of interest categories. Our technology dynamically inserts those advertisers' pre- and mid-roll ads into the relevant videos and delivers the ads to the audience targeted by those advertisers. We may pay content partners a portion of our advertising revenue for the right to use and distribute their content on our platform.

We plan to continue to focus our investment in features that differentiate Twitter and capitalize on our unique value proposition for advertisers, including video and more organic ad formats.

Our technology platform and information database enable us to provide targeting capabilities based on audience attributes like geography, interests, keyword, television conversation, content, event and devices that make it possible for advertisers to promote their brands, products and services, amplify their visibility and reach, and complement and extend the conversation around their advertising campaigns.

Our platform also allows customers to advertise across the mobile ecosystem, both on Twitter’s owned and operated properties as well as off Twitter on third partythird-party publishers’ websites, applications and other offerings, across the full user lifecycle — from acquiring new users to engaging existing users. We enable advertisers to extend their reach beyond Twitter through:

Products for Developers

We provide a set of tools, public APIs and embeddable widgets that developers can use to contribute their content to our platform, syndicate and distribute Twitter content across their properties and enhance their websites and applications with Twitter content. Websites integrating with Twitter add value to our user experience. Indeed manyMany applications have been registered by developers to enable them to integrate with our platform, and leverage Twitter content to enhance and extend their applications in new and creative ways. The goal of our platform product development is to make it easy for developers to integrate seamlessly with Twitter.

Products for Data Partners

We offer subscription access to our public data feed for partners who wish to access data beyond our public API, which offers a limited amount of our public data for free. In 2017, we introduced premium APIs, a new product line that provides developers with increased access to Twitter data and a more flexible way to build and scale their businesses. Our data products and services offer more sophisticated data sets and better data enrichments to allow developers and businesses to utilize our public content to derive business insights and build products using the unique content that is shared on Twitter. We plan to takeare taking steps to grow our data licensing revenue with a more brand-centric approach to channels, markets, products, and pricing. We believe this approach will position both Twitter and our key channel partners for greater growth and monetization, and we are investing in deeper partnerships with a few select solution providers to help brands realize greater value from our data and platform.

Competition

Our business is characterized by rapid technological change, frequent product innovation and continuously evolving user, advertiser, content partner, platform partner and developer preferences and expectations. We face significant competition in every aspect of our business, including from companies that provide tools to facilitate communications and the sharing of information, companies that enable marketers to display advertising, and other online ad networks, exchanges and platforms. We also compete to attract, engage, and retain people who use our products, to attract and retain marketers, and to attract and retain developers to build compelling mobile and web applications that integrate with our products. We have seen escalating competition for digital ad spending and expect this trend to continue. We also compete to attract and retain employees, especially software engineers, designers, and product managers.

We compete with the following companies:companies for users’ attention and for advertisers’ budgets:

As we introduce new products, as our existing products evolve, or as other companies introduce new products and services, we may become subject to additional competition.

Our industry is evolving rapidly and is becoming increasingly competitive. See the sections titled “Risk Factors—If we are unable to compete effectively for users and advertiser spend, our business and operating results could be harmed” and “Risk Factors—We depend on highly skilled personnel to grow and operate our business, and if we are unable to hire, retain and motivate our personnel, we may not be able to grow effectively.”  

Technology,Technology, Research and Development

Twitter is composed of a set of core, scalable and distributed services that are built from proprietary and open source technologies. These systems are capable of delivering billions of short messages to hundreds of millions of people a day in an efficient and reliable way. We continue to invest in our existing products and services as well as develop new products and services through research and product development.

Sales and Marketing

We have a global sales force and sales support staff that is focused on attracting and retaining advertisers while certain advertisers use our self-serve advertising platform to launch and manage their advertising campaigns. Our sales force and sales support staff assistsassist advertisers throughout the advertising campaign cycle, from pre-purchase decision making to real-time optimizations as they utilize our campaign management tools, and to post-campaign analytics reports to assess the effectiveness of their advertising campaigns. In the fourth quarter of 2016, the company reorganized the company’s sales, partnerships, and marketing efforts, intended to create greater focus and efficiency.

Since our inception, our user base has grown primarily by word-of-mouth. Prior to 2015, we built our brand through these efforts and increased usage of Twitter worldwide with relatively minimal marketing costs. Beginning in 2015, we complemented that organic growth with targeted campaigns to drive new user acquisition. Then, from late 2016, we've shifted someWe set out to clearly define who we are and express the uniqueness and power of that focus toour brand through marketing campaigns to drive awareness of Twitter'sTwitter’s unique positioning around “What's“What’s Happening Now”. In 2017, our marketing campaign “SeeEverySide” demonstrated how Twitter differs from other social platforms.

Intellectual Property

We seek to protect our intellectual property rights by relying on federal, state and common law rights in the United States and other countries, as well as contractual restrictions. We generally enter into confidentiality and invention assignment agreements with our employees and contractors, and confidentiality agreements with other third parties, in order to limit access to, and disclosure and use of, our confidential information and proprietary technology. In addition to these contractual arrangements, we also rely on a combination of trademarks, trade dress, domain names, copyrights, trade secrets and patents to help protect our brand and our other intellectual property.

As of December 31, 2016, we had 1,035 issued patents in the United States and foreign countries relating to message distribution, graphical user interfaces, security and related technologies. Our issued United States patents are expected to expire between 2017 and 2034.

We may be unable to obtain patent or trademark protection for our technologies and brands, and our existing patents and trademarks, and any patents or trademarks that may be issued in the future, may not provide us with competitive advantages or distinguish our products and services from those of our competitors. In addition, any patents and trademarks may be contested, circumvented or found unenforceable or invalid, and we may not be able to prevent third parties from infringing, diluting or otherwise violating them.

In May 2013, we implemented our Innovator’s Patent Agreement, or IPA, which we enter into with our employees and consultants, including our founders. We implemented the IPA because we were concerned about the proliferation of offensive patent lawsuits, including lawsuits by “non-practicing entities.” We are also encouraging other companies to implement the IPA in an effort to reduce the number of patents with offensive rights that may be transferred to third parties, including non-practicing entities. We believe that a reduction in the number of patents with transferrable offensive rights may reduce the number of offensive lawsuits that may be filed, particularly by non-practicing entities.

The IPA limitswhich applies to our current and future patents, allows us to assert our patents defensively. The IPA also allows us to assert our patents offensively with the permission of the inventors of the applicable patent. The IPA can limit our ability to prevent infringement of our patents. See the section titled “Risk Factors—Our intellectual property rights are valuable, and any inability to protect them could reduce the value of our products, services and brand” for a further discussion of the IPA.

Companies in the internet, technology and media industries own large numbers of patents, copyrights, trademarks and trade secrets, and frequently enter into litigation based on allegations of infringement, misappropriation, or other violations of intellectual property or other rights. In addition, various “non-practicing entities” that own patents and other intellectual property rights often attempt to aggressively assert their rights in order to extract value from technology companies. We are presently involved in a number of intellectual property lawsuits, and from time to time we face, and we expect to face in the future, allegations that we have infringed or otherwise violated the patents, copyrights, trademarks, trade secrets, and other intellectual property rights of third parties, including our competitors and non-practicing entities. As we face increasing competition, we will likely face more intellectual property-related claims and litigation matters. For additional information, see the sections titled “Risk Factors—We are currently, and expect to be in the future, party to intellectual property rights claims that are expensive and time consuming to defend, and, if resolved adversely, could have a significant impact on our business, financial condition or operating results” and ���Legal Proceedings.”  

Government Regulation

We are subject to a number of U.S. federal and state and foreign laws and regulations that involve matters central to our business. These laws and regulations may involve privacy, rights of publicity, data protection, content regulation, intellectual property, competition, protection of minors, consumer protection, taxation or other subjects. Many of these laws and regulations are still evolving and being tested in courts and could be interpreted in ways that could harm our business. In addition, the application and interpretation of these laws and regulations often are uncertain, particularly in the new and rapidly evolving industry in which we operate.

We are also subject to federal, state and foreign laws regarding privacy and the protection of user data. Foreign data protection, privacy, consumer protection, content regulation and other laws and regulations are often more restrictive than those in the United States. For example, the General Data Protection Regulation, or the GDPR, has been adopted and will go into effect in May 2018. The GDPR also includes more stringent operational requirements for entities processing personal information and significant penalties for non-compliance. There are also a number of legislative proposals pending before the U.S. Congress, various state legislative bodies and foreign governments concerning content regulation and data protection that could affect us. For example, regulation relating to the General Data Protection Regulation has been adopted by European legislative bodies that will be effective in May 2018 and will include more stringent operational requirements for entities processing personal information and significant penalties for non-compliance.

In March 2011, to resolve an investigation into various incidents, we entered into a settlement agreement with the Federal Trade Commission, or FTC, that, among other things, requires us to establish an information security program designed to protect non-public consumer information and also requires that we obtain biennial independent security assessments. The FTC investigation was the result of two separate incidents in which unauthorized intruders obtained administrative passwords of certain Twitter employees. In one of the incidents, the intruder accessed the employee’s administrative capabilities to fraudulently reset various user passwords and post unauthorized Tweets. The obligations under the settlement agreement remain in effect until the later of March 2, 2031, or the date 20 years after the date, if any, on which the U.S. government or the FTC files a complaint in federal court alleging any violation of the order. Violation of existing or future regulatory orders, settlements, or consent decrees could subject us to substantial monetary fines and other penalties that could negatively affect our financial condition and results of operations.

Twitter users may be restricted from accessing Twitter from certain countries, and other countries have intermittently restricted access to Twitter. For example, Twitter is not directly accessible in China and has been blocked in the past in Turkey. It is possible that other governments may seek to restrict access to or block our website or mobile applications, censor content available through our products or impose other restrictions that may affect the accessibility or usability of Twitter for an extended period of time or indefinitely. For instance, some countries have enacted laws that allow websites to be blocked for hosting certain types of content.

For additional information, see the section titled “Risk Factors—Our business is subject to complex and evolving U.S. and foreign laws and regulations. These laws and regulations are subject to change and uncertain interpretation, and could result in claims, changes to our business practices, monetary penalties, increased cost of operations or declines in user growth, user engagement or ad engagement, or otherwise harm our business.”

Seasonality

Advertising spending is traditionally strongest in the fourth quarter of each year. Historically, this seasonality in advertising spending has affected our quarterly results, with higher sequential advertising revenue growth from the third quarter to the fourth quarter compared to sequential advertising revenue growth from the fourth quarter to the subsequent first quarter.

Information about Segment and Geographic Revenue

Information about segment and geographic revenue is set forth in Note 17 of the Notes to Consolidated Financial Statements under Item 8 of this Annual Report on Form 10-K.

Employees

As of December 31, 2016,2017, we had 3,5833,372 full-time employees.

Corporate Information

We were incorporated in Delaware in April 2007. Our principal executive offices are located at 1355 Market Street, Suite 900, San Francisco, California 94103, and our telephone number is (415) 222-9670. We completed our initial public offering in November 2013 and our common stock is listed on the New York Stock Exchange under the symbol “TWTR.” Unless the context requires otherwise, the words “Twitter,” “we,” “Company,” “us” and “our” refer to Twitter, Inc. and our wholly owned subsidiaries.

Available Information

Our website is located at www.twitter.com, and our investor relations website is located at http://investor.twitterinc.com/. Copies of our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, and amendments to these reports filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, are available, free of charge, on our investor relations website as soon as reasonably practicable after we file such material electronically with or furnish it to the Securities and Exchange Commission, or the SEC. The SEC also maintains a website that contains our SEC filings. The address of the site is www.sec.gov. Further, a copy of this Annual Report on Form 10-K is located at the SEC’s Public Reference Room at 100 F Street, NE, Washington, D.C. 20549. Information on the operation of the Public Reference Room can be obtained by calling the SEC at 1-800-SEC-0330.

We webcast our earnings calls and certain events we participate in or host with members of the investment community on our investor relations website. Additionally, we provide notifications of news or announcements regarding our financial performance, including SEC filings, investor events, press and earnings releases, and blogs as part of our investor relations website. We have used, and intend to continue to use, our investor relations website, as well as certain Twitter accounts (@jack, @twitter and @twitterIR), as means of disclosing material non-public information and for complying with our disclosure obligations under Regulation FD. Further corporate governance information, including our certificate of incorporation, bylaws, corporate governance guidelines, board committee charters, and code of business conduct and ethics, is also available on our investor relations website under the heading “Corporate governance.” The contents of our websites are not intended to be incorporated by reference into this Annual Report on Form 10-K or in any other report or document we file with the SEC, and any references to our websites are intended to be inactive textual references only.

Item 1A. RISK FACTORS

Investing in our common stock involves a high degree of risk. You should carefully consider the risks and uncertainties described below, together with all of the other information in this Annual Report on Form 10-K, including the section titled “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our consolidated financial statements and related notes, before making a decision to invest in our common stock. The risks and uncertainties described below may not be the only ones we face. If any of the risks actually occurs, our business, financial condition, operating results, cash flows and prospects could be materially and adversely affected. In that event, the market price of our common stock could decline, and you could lose part or all of your investment.

Risks Related to Our Business and Our Industry

If we fail to grow our user base, or if user engagement or ad engagement on our platform decline, our revenue, business and operating results may be harmed.

The size of our user base and our users’ level of engagement are critical to our success. We had 319330 million average MAUs in the three months ended December 31, 2017, representing a 4% increase from 318 million average MAUs in the three months ended December 31, 2016 representing a 4% increase from 305 million average MAUs in the three months ended December 31, 2015. DAU(see section entitled “Management’s Discussion and Analysis of Financial Condition and Results of Operations – Note About Our MAU Adjustment” below). DAUs for the three months ended December 31, 2016 grew 11% year over year.2017 increased 12% year-over-year. Our financial performance has been and will continue to be significantly determined by our success in growing the number of users and increasing their overall level of engagement on our platform as well as the number of ad engagements; however, we expect revenue growth will lag behind user growth.engagements. We anticipate that our user growth rate will continue to slow over time as the size of our user base increases. For example, in general, a higher proportion of Internet users in the United States uses Twitter than Internet users in other countries and, in the future, we expect our user growth rate in certain international markets such as Canada, France, Germany, India, Japan, Mexico, the Philippines, Saudi Arabia, and South Korea, to continue to be higher than our user growth rate in the United States. To the extent our logged-in user growth rate slows, our success will become increasingly dependent on our ability to increase levels of ad engagement on Twitter and monetizing our total audience on logged-out usage and syndicated properties as well as increasing revenue growth from the sale to advertisers of our advertising products which we place on Twitter properties and third party publishers’ websites, applications and other offerings.Twitter. We generate a substantial majority of our revenue based upon engagement by our users with the ads that we display. If people do not perceive our products and services to be useful, reliable and trustworthy, we may not be able to attract users or increase the frequency of their engagement with our platform and the ads that we display. A number of consumer-oriented websites or platforms that achieved early popularity have seen their user bases or levels of engagement decline, in some cases precipitously. There is no guarantee that we will not experience a similar erosion of our user base or engagement levels. A number of factors could potentially negatively affect user growth and engagement, including if:

We believe that returning to meaningful MAU growth in audience and engagement is dependent on improving our product and feature offerings to demonstrate our value proposition to a larger audience. If we are unable to increase our user base, user growth rate or user engagement, or if these metrics decline, our products and services could be less attractive to potential or new users, as well as to advertisers, content partners and platform partners, which would have a material and adverse impact on our business, financial condition and operating results.

If our users or content partners do not continue to contribute content or such content is not viewed as unique or engaging by other users, we may experience a decline in the number of users accessing our products and services and user engagement, which could result in the loss of content partners, advertisers, platform partners and revenue.

Our success depends on our ability to provide users of our products and services with unique and engaging content, which in turn depends on the content contributed by our users. We believe that one of our competitive advantages is the quality, quantity and real-time nature of the content on Twitter, and that access to unique or real-time content is one of the main reasons users visit Twitter. We seek to foster a broad and engaged user community, and we encourage world leaders, government officials, celebrities, athletes, journalists, sports teams, media outlets and brands to use our products and services to express their views to broad audiences. We also encourage media outlets to use our products and services to distribute their content. In addition, we license our premium live streaming video content from a variety of content providers.  If these content providers are no longer willing or able to license us content upon economic and other terms that are acceptable to us, our ability to stream such content will be adversely affected and/or our costs could increase.  If users, including influential users, do not continue to contribute content or content providers do not license content to Twitter, and we are unable to provide users with unique, engaging and timely content, our user base and user engagement may decline. Additionally, if we are not able to address user concerns regarding the safety and security of our products and services or if we are unable to successfully prevent abusive or other hostile behavior on our platform, the size of our user base and user engagement may decline. We rely on the sale of advertising services for the substantial majority of our revenue and a decline in the number of users, user growth rate, or user engagement, including as a result of the loss of world leaders, government officials, celebrities, athletes, journalists, sports teams, media outlets and brands who generate content on Twitter, advertisers may deter new advertisers from using our products or services or cause current advertisers to reduce their spending with us or cease doing business with us, which would harm our business and operating results.

We generate the substantial majority of our revenue from advertising. The loss of advertising revenue could harm our business.

The substantial majority of our revenue is currently generated from third parties advertising on Twitter. We generated approximately 90%89% and 89%86% of our revenue from advertising in the fiscal years ended December 31, 20152016 and 2016,2017, respectively. We generate substantially all of our advertising revenue through the sale of our three Promoted Products: Promoted Tweets, Promoted Accounts and Promoted Trends. As is common in our industry, our advertisers do not have long-term advertising commitments with us. In addition, many of our advertisers purchase our advertising services through one of several large advertising agency holding companies. To sustain or increase our revenue, we must add new advertisers and encourage existing advertisers to maintain or increase the amount of advertising inventory purchased through our platform and adopt new features and functionalities that we add to our platform. However, advertising agencies and potential new advertisers may view our Promoted Products or any new products or services we offer as experimental and unproven, and we may need to devote additional time and resources to educate them about our products and services. Advertisers also may choose to reach users through our free products and services, instead of our Promoted Products. Advertisers will not continue to do business with us, or they will reduce the prices they are willing to pay to advertise with us, if we do not deliver ads in an effective manner, or if they do not believe that their investment in advertising with us will generate a competitive return on investment relative to alternatives, including online, mobile and traditional advertising platforms. In addition, competition for advertising is becoming increasingly more intense and our advertising revenue could be further impacted by escalating competition for digital ad spending as well as the re-evaluation of our revenue product feature portfolio, which could result in the de-emphasis of certain product features. Since our initial public offering, our revenue growth has been primarily driven by increases in the number of our users and increases in our ad load driven by strong advertiser demand as well as other factors. To date, our available advertising inventory has been greater than demand. Our future revenue growth, however, may be limited by available advertising inventory for specific ad types on certain days if we do not increase the number of our users, their engagement or monetize our larger global audience. Our advertising revenue also could be adversely affected by a number of other factors, including:

The occurrence of any of these or other factors could result in a reduction in demand for our ads, which may reduce the prices we receive for our ads, either of which would negatively affect our revenue and operating results.

If we are unable to compete effectively for users and advertiser spend, our business and operating results could be harmed.

Competition for users of our products and services is intense. Although we have developed a global platform that we believe is the best and fastest place to see what’s happening and what people are talking about all around the world, we face strong competition in our business. We compete against many companies to attract and engage users, including companies which have greater financial resources and substantially larger user bases, such as Facebook (including Instagram and WhatsApp), Alphabet (including Google (includingand YouTube), Microsoft (including LinkedIn), Snap and Yahoo,Oath (formerly known as Yahoo), which offer a variety of Internet and mobile device-based products, services and content. For example, Facebook operates a social networking site with significantly more users than Twitter and has been introducing features similar to those of Twitter. In addition, GoogleAlphabet may use its strong position in one or more markets to gain a competitive advantage over us in areas in which we operate, including by integrating competing features into products or services they control. As a result, our competitors may draw users towards their products or services and away from ours. This could decrease the growth or engagement of our user base, which, in turn, would negatively affect our business. We also compete against largely regional social media and messaging companies that have strong positions in particular countries such as Kakao and Line.

We believe that our ability to compete effectively for users depends upon many factors both within and beyond our control, including:

We also face significant competition for advertiser spend. The substantial majority of our revenue is currently generated through third parties advertising on Twitter, and we compete against online and mobile businesses, including those referenced above, and traditional media outlets, such as television, radio and print, for advertising budgets. In addition, many advertisers, particularly branded advertisers, use marketing mix analyses to determine how to allocate their advertising budgets on an annual or bi-annual basis.  Accordingly, if we fail to demonstrate to such advertisers during the appropriate time period that we provide a better return on investment than our competitors do, we may lose the opportunity to secure, increase or sustain our share of the advertising budget allocated for a significant portion of the year until the next budget cycle.  

We also compete with advertising networks, exchanges, demand side platforms and other platforms, such as Google AdSense, DoubleClick Ad Exchange, YahooNexage and Brightroll Ad Exchange,Exchanges, Oath (formerly known as AOL’s Ad.comAd.com) and Microsoft Media Network, for marketing budgets and in the development of the tools and systems for managing and optimizing advertising campaigns. In order to grow our revenue and improve our operating results, we must increase our share of spending on advertising relative to our competitors, many of which are larger companies that offer more traditional and widely accepted advertising products. In addition, some of our larger competitors have substantially broader product or service offerings and leverage their relationships based on other products or services to gain additional share of advertising budgets.

We believe that our ability to compete effectively for advertiser spend depends upon many factors both within and beyond our control, including:

In recent years, there have been significant acquisitions and consolidation by and among our actual and potential competitors. We anticipate this trend of consolidation will continue, which will present heightened competitive challenges for our business. Acquisitions by our competitors may result in reduced functionality of our products and services. For example, following Facebook’s acquisition of Instagram, Facebook disabled Instagram’s photo integration with Twitter such that Instagram photos were no longer viewable within Tweets and users are instead re-directed to Instagram to view Instagram photos through a link within a Tweet. As a result, our users may be less likely to click on links to Instagram photos in Tweets, and Instagram users may be less likely to Tweet or remain active users of Twitter. Any similar elimination of integration with Twitter in the future, whether by Facebook or others, may adversely impact our business and operating results.

Consolidation may also enable our larger competitors to offer bundled or integrated products that feature alternatives to our platform. Reduced functionality of our products and services, or our competitors’ ability to offer bundled or integrated products that compete directly with us, may cause our user growth, user engagement and ad engagement to decline and advertisers to reduce their spend with us.

If we are not able to compete effectively for users and advertiser spend our business and operating results would be materially and adversely affected.

Our operating results may fluctuate from quarter to quarter, which makes them difficult to predict.

Our quarterly operating results have fluctuated in the past and will fluctuate in the future. As a result, our past quarterly operating results are not necessarily indicators of future performance. Our operating results in any given quarter can be influenced by numerous factors, many of which we are unable to predict or are outside of our control, including:

Given our limited operating history and the rapidly evolving markets in which we compete, our historical operating results may not be useful to you in predicting our future operating results. AsIf our revenue growth rate slows, we expect that the seasonality in our business may become more pronounced and may in the future cause our operating results to fluctuate. For example, advertising spending is traditionally seasonally strong in the fourth quarter of each year and we believe that this seasonality affects our quarterly results, which generally reflect higher sequential advertising revenue growth from the third to fourth quarter compared to sequential advertising revenue growth from the fourth quarter to the subsequent first quarter. In addition, global economic concerns continue to create uncertainty and unpredictability and add risk to our future outlook. An economic downturn in any particular region in which we do business or globally could result in reductions in advertising revenue, as our advertisers reduce their advertising budgets, and other adverse effects that could harm our operating results.

We depend on highly skilled personnel to grow and operate our business, and have seen high levels of attrition.  If we are unable to hire, retain and motivate our personnel, we may not be able to grow effectively.

Our future success and strategy will depend upon our continued ability to identify, hire, develop, motivate and retain highly skilled personnel, including senior management, engineers, designers and product managers. We depend on contributions from our employees, and in particular our senior management team, to execute efficiently and effectively. We do not have employment agreements other than offer letters with any member of our senior management or other key employee, and we do not maintain key person life insurance for any employee. We also face significant competition for employees, particularly in the San Francisco Bay Area (where our headquarters is located), and other key markets, for engineers, designers and product managers from other Internet and high-growth companies, which include both publicly-traded and privately-held companies. As a result, we may not be able to retain our existing employees or hire new employees quickly enough to meet our needs. At the same time, we are also experiencing high voluntary attrition, and the resulting influx of new leaders and other employees requiresmay require that we expend the time, attention and resources necessary to recruit and retain talent, restructure parts of our organizations,organization, and train and integrate new employees. In addition, to attract highly and retain skilled personnel, we have had to offer, and believe we will need to continue to offer, highly competitive compensation packages. Identifying, recruiting, training and integrating qualified individuals will require significant time, expense and attention. We may need to invest significant amounts of cash and equity to attract and retain new employees and we may nevernot realize returnssufficient return on these investments. In addition, changes to U.S. immigration and work authorization laws and regulations can be significantly affected by political forces and levels of economic activity. Our business may be materially adversely affected if legislative or administrative changes to immigration or visa laws and regulations impair our hiring processes or projects involving personnel who are not citizens of the country where the work is to be performed. If we are not able to effectively attract and retain employees, we may not be able to innovate or execute quickly on our strategy and our ability to achieve our strategic objectives will be adversely impacted, and our business will be harmed.

We also believe that our culture and core values have been, and will continue to be, a key contributor to our success and our ability to foster the innovation, creativity and teamwork we believe we need to support our operations.  As we continue to evolve, however, we are subject to the risks of over-hiring and over-compensating our employees, and to the challenges of integrating, developing and motivating an employee base that is located in various countries around the world.  If we fail to effectively manage our hiring needs and successfully integrate our new hires, our efficiency and ability to meet our forecasts and our culture, employee morale, productivity and retention could suffer, and our business and operating results could be adversely affected.

If we fail to monetize effectively in international markets, our revenue and our business will be harmed.

We may not be able to monetize our products and services internationally as effectively as in the United States as a result of competition, advertiser demand, differences in the digital advertising market and digital advertising conventions, as well as differences in the way that users in different countries access or utilize our products and services. For example, a significant portion of users in emerging markets like India and Pakistan use feature phones and communicate via SMS messaging, both of which have limited functionality and neither of which may be able to take full advantage of our products and services offered on smartphone or our website or desktop applications. Users who access Twitter through SMS messaging may monetize at lower rates than other users. Differences in the competitive landscape in international markets may impact our ability to monetize our products and services. For example, in South Korea we face intense competition from a messaging service offered by Kakao, which offers some of the same communication features as Twitter. The existence of a well-established competitor in an international market may adversely affect our ability to increase our user base, attract content partners, advertisers and platform partners and monetize our products in such market. We may also experience differences in advertiser demand in international markets. For example, during times of political upheaval, advertisers may choose not to advertise on Twitter. Certain international markets are also not as familiar with digital advertising in general, or in new forms of digital advertising such as our Promoted Products. Further, we face challenges in providing certain advertising products, features or analytics in certain international markets, such as the European Union, due to government regulation. Our products and services may also be used differently abroad than in the United States. In particular, in certain international markets where Internet access is not as rapid or reliable as in the United States, users tend not to take advantage of certain features of our products and services, such as rich media included in Tweets, video or live streaming video. The limitation of mobile devices of users in emerging and other markets limits our ability to deliver certain features to those users and may limit the ability of advertisers to deliver compelling advertisements to users in these markets which may result in reduced ad engagements which would adversely affect our business and operating results.

If our revenue from our international operations, and particularly from our operations in the countries and regions where we have focused our spending, does not exceed the expense of establishing and maintaining these operations, our business and operating results will suffer. In addition, our user base may expand more rapidly in international regions where we are less successful in monetizing our products and services. As our user base continues to expand internationally, we will need to increase revenue from the activity generated by our international users in order to grow our business. For example, users outside the United States constituted 79% of our average MAUs in the three months ended December 31, 2016,2017, but our international revenue, as determined based on the billing location of our advertisers, was only 39%44% of our consolidated revenue in the three months ended December 31, 2016.2017. Our inability to successfully expand our business internationally could adversely affect our business, financial condition and operating results.

User growth and engagement depend upon effective interoperation with operating systems, networks, devices, web browsers and standards that we do not control.

We make our products and services available across a variety of operating systems and through websites. We are dependent on the interoperability of our products and services with popular devices, desktop and mobile operating systems and web browsers that we do not control, such as Mac OS, Windows, Android, iOS, Chrome and Firefox. Any changes, bugs or technical issues in such systems, devices or web browsers or changes in our relationships with mobile operating system partners or mobile carriers, or in their terms of service or policies that degradediminish the functionality of our products and services, make it difficult for our users to access our content, limit our ability to target or measure the effectiveness of ads, impose fees related to our products or services or give preferential treatment to competitive products or services could adversely affect usage of our products and services. For example, many of our relationships with our mobile carriers to deliver our SMS messages were originally negotiated as free or low-cost connections, but recently some of the mobile carriers have been proposing fee increases for these arrangements, which may not be cost-effective for us. This may, in turn, adversely affect the number of users who receive our SMS messages. Additionally, some of our mobile carriers have experienced infrastructure issues due to natural disasters, which have caused deliverability errors or poor quality communications with our products. Any such errors, regardless of whether caused by our infrastructure or that of the service provider, may result in the loss of our existing users or may make it difficult to attract new users. Further, if the number of platforms for which we develop our product expands, it will result in an increase in our operating expenses. In order to deliver high quality products and services, it is important that our products and services work well with a range of operating systems, networks, devices, web browsers and standards that we do not control. In addition, because a majority of our users access our products and services through mobile devices, we are particularly dependent on the interoperability of our products and services with mobile devices and operating systems. systems in order to deliver our products and services. For example, a recent change was made to Safari’s integration with third-party applications including Twitter that resulted in a decrease of approximately 2 million MAUs who accessed Twitter by using registered third-party applications when those applications automatically contact our servers for regular updates without discernible user-initiated action. We also may not be successful in developing relationships with key participants in the mobile industry or in developing products or services that operate effectively with these operating systems, networks, devices, web browsers and standards. In the event that it is difficult for our users to access and use our products and services, particularly on their mobile devices, our user growth and engagement could be harmed, and our business and operating results could be adversely affected.

Our ability to convince potential and new users of the value of our products and services is critical to increasing our user base and to the success of our business.

We have developed a global platform that we believe is the best and fastest place to see what’s happening and what people are talking about all around the world, but the market for our products and services is relatively new and may not develop as expected, if at all. Despite our efforts to reduce barriers to consumption, people who are not our users may not understand the value of our products and services and new users may initially find our productproducts confusing, which may make retention of such users more difficult. There may be a perception that our products and services are only useful to users who Tweet, or to influential users with large audiences. Convincing potential and new users of the value of our products and services is critical to increasing our user base and to the success of our business.

If we fail to educate potential users and potential advertisers about the value of our products and services, if the market for our platform does not develop as we expect or if we fail to address the needs of this market, our business will be harmed. We may not be able to successfully address these risks and challenges or others. Failure to adequately address these risks and challenges could harm our business and cause our operating results to suffer.

We have incurred significant operating losses in the past, and we may not be able to achieve or subsequently maintain profitability.

Since our inception, we have incurred significant operating losses, and, as of December 31, 2016,2017, we had an accumulated deficit of $2.55$2.67 billion. Although our revenue has grown rapidly, increasing from $664.9 million in 2013 to $2.53$2.44 billion in 2016, we expect that2017, our revenue growth rate will slow in the futurehas slowed as a result of a variety of factors, including the decline in the growth rate of our user base.factors. We believe that our future revenue growth will depend on, among other factors, our ability to attract new users, increase user engagement and ad engagement, increase our brand awareness, compete effectively, maximize our sales efforts, demonstrate a positive return on investment for advertisers, and successfully develop new products and services. Accordingly, you should not rely on the revenue growth of any prior quarterly or annual period as an indication of our future performance. Our costs may increase in future periods as we continue to expend substantial financial resources on:

These investments may not result in increased revenue or growth in our business. Additionally, certain new revenue products or product features may carry higher costs relative to our other products, which may decrease our margins. If we are unable to generate adequate revenue growth and to manage our expenses, we may continue to incur significant losses in the future and may not be able to achieve or maintain profitability.

Our business depends on continued and unimpeded access to our products and services on the Internet by our users, content partners, advertisers, and platform partners. If we or our users experience disruptions in Internet service or if Internet service providers are able to block, degrade or charge for access to our products and services, we could incur additional expenses and the loss of users and advertisers.

We depend on the ability of our users, content partners, advertisers and platform partners to access the Internet. Currently, this access is provided by companies that have significant market power in the broadband and Internet access marketplace, including incumbent telephone companies, cable companies, mobile communications companies, government-owned service providers, device manufacturers and operating system providers, any of whom could take actions that degrade, disrupt or increase the cost of user access to our products or services, which would, in turn, negatively impact our business. The adoption or repeal of any laws or regulations that adversely affect the growth, popularity or use of the Internet, including laws or practices limiting Internet neutrality, could decrease the demand for, or the usage of, our products and services, increase our cost of doing business and adversely affect our operating results. For example, access to Twitter is blocked in China and has been intermittently blocked in Turkey in the last three years.years and certain of our SMS messages have been blocked in Saudi Arabia. We also rely on other companies to maintain reliable network systems that provide adequate speed, data capacity and security to us and our users. As the Internet continues to experience growth in the number of users, frequency of use and amount of data transmitted, the Internet infrastructure that we and our users rely on may be unable to support the demands placed upon it. The failure of the Internet infrastructure that we or our users rely on, even for a short period of time, could undermine our operations and harm our operating results.

Our new products, product features, services and initiatives and changes to existing products, services and initiatives could fail to attract users, content partners, advertisers and platform partners or generate revenue.

Our industry is subject to rapid and frequent changes in technology, evolving customer needs and the frequent introduction by our competitors of new and enhanced offerings. We must constantly assess the playing field and determine whether we need to improve or re-allocate resources amongst our existing products and services or create new ones (independently or in conjunction with third parties). Our ability to increase the size and engagement of our user base, attract content partners, advertisers and platform partners and generate revenue will depend on those decisions. We may introduce significant changes to our existing products and services or develop and introduce new and unproven products and services, including technologies with which we have little or no prior development or operating experience. For example, in 2015, we introduced Periscope, a mobile application that lets users share and experience live video from their mobile phones and in 2013, we introduced Vine, a mobile application that enablesenabled users to create and distribute videos that are up to six seconds in length, which we discontinued in January 2017 but transitioned certain product features to the Vine Camera app. Also, we recently introduced new features to Twitter such as “Moments”, a curated collection of Tweets, photos, videos, and Periscope broadcasts about current news stories or events; “In Case You Missed It,” which surfaces Tweets a logged-in user may have missed since last accessing Twitter; expanding our character limit to 280 characters for more people around the world; and Instant Timeline, which helps create a timeline for“Threads,” new users as well as new featuresfeature that allows people to our Promotedmore easily thread Tweets like promoted video ads.together. If new or enhanced products, product features or services fail to engage users, content partners and advertisers, we may fail to attract or retain users or to generate sufficient revenue or operating profit to justify our investments, and our business and operating results could be adversely affected. In addition, we have launched and expect to continue to launch strategic initiatives that do not directly generate revenue but which we believe will enhance our attractiveness to users, content partners and advertisers. In the future, we may invest in new products, product features, services and initiatives to generate revenue, but there is no guarantee these approaches will be successful. We may not be successful in future efforts to generate revenue from our new products or services. If our strategic initiatives do not enhance our ability to monetize our existing products and services, or enable us to develop new approaches to monetization or meet the expectations of our users or third-party business partners, we may not be able to maintain or grow our revenue or recover any associated development costs and our operating results could be adversely affected.

If we fail to effectively manage changes to our business and operations, our business and operating results could be harmed.

Providing our products and services to our users is costly and we expect certain of our expenses to continue to increase in the future as we broaden our user base and increase user engagement, as users increase the amount of content they contribute, and as we develop and implement new features, products and services that require more infrastructure, in particular our video product features. In addition, our operating expenses, such as our research and development expenses and sales and marketing expenses, have grown rapidly as we have expanded our business. Historically, our costs have increased each year due to these factors and we expect to continue to incur increasing costs to support our operations. We expect to continue to invest in our infrastructure so that we can provide our products and services rapidly and reliably to users around the world, including in countries where we do not expect significant near-term monetization.

In the fourth quarter of 2016, we implemented a restructuring and reduction in force to continue to better align our operating expenses with our revenue, manage our costs better, and more efficiently manage our business.  We intend to fully invest in our highest priorities, while eliminating investment in noncore areas. Finding and maintaining the appropriate balance will require significant expenditures and allocation of valuable management resources. If we fail to achieve the necessary level of efficiency in our organization, our business, operating results and financial condition would be harmed.

We focus on product innovation and user engagement rather than short-term operating results.

We encourage employees to quickly develop and help us launch new and innovative features. We focus on improving the user experience for our products and services, which includes protecting user privacy, and on developing new and improved products and services for the advertisers on our platform. We prioritize innovation and the experience for users and advertisers on our platform over short-term operating results. We frequently make product, product feature and service decisions that may reduce our short-term operating results if we believe that the decisions are consistent with our goals to improve the user experience and performance for advertisers, which we believe will improve our operating results over the long term. For example, we are investing in our new live-streaming video experiences, and we may not successfully monetize such experiences. These decisions may not be consistent with the short-term expectations of investors and may not produce the long-term benefits that we expect, in which case our user growth and user engagement, our relationships with advertisers and our business and operating results could be harmed. In addition, our focus on the user experience may negatively impact our relationships with our existing or prospective advertisers. This could result in a loss of advertisers, which could harm our revenue and operating results.

Our business and operating results may be harmed by a disruption in our service, or by our failure to timely and effectively scale and adapt our existing technology and infrastructure.

One of the reasons people come to Twitter is for real-time information. We have experienced, and may in the future experience, service disruptions, outages and other performance problems due to a variety of factors, including infrastructure changes, human or software errors, hardware failure, capacity constraints due to an overwhelming number of people accessing our products and services simultaneously, computer viruses and denial of service or fraud or security attacks. For instance, in January 2016, we experienced a brief service outage during which Twitter.com and Twitter mobile clients were inaccessible as a result, in part, of a software misconfiguration in one of our infrastructure components. Additionally, although we are investing significantly to improve the capacity, capability and reliability of our infrastructure, we are not currently serving traffic equally through our co-located data centers that support our platform. Accordingly, in the event of a significant issue at the data center supporting most of our network traffic, some of our products and services may become inaccessible to the public or the public may experience difficulties accessing our products and services. Any disruption or failure in our infrastructure could hinder our ability to handle existing or increased traffic on our platform, which could significantly harm our business.

As the number of our users increases and our users generate more content, including photos and videos hosted by Twitter, we may be required to expand and adapt our technology and infrastructure to continue to reliably store, serve and analyze this content. It may become increasingly difficult to maintain and improve the performance of our products and services, especially during peak usage times, as our products and services become more complex and our user traffic increases. In addition, because we lease our data center facilities, we cannot be assured that we will be able to expand our data center infrastructure to meet user demand in a timely manner, or on favorable economic terms. If our users are unable to access Twitter or we are not able to make information available rapidly on Twitter, users may seek other channels to obtain the information, and may not return to Twitter or use Twitter as often in the future, or at all. This would negatively impact our ability to attract users, content partners and advertisers and increase engagement of our users. We expect to continue to make significant investments to maintain and improve the capacity, capability and reliability of our infrastructure. To the extent that we do not effectively address capacity constraints, upgrade our systems as needed and continually develop our technology and infrastructure to accommodate actual and anticipated changes in technology, our business and operating results may be harmed.

If we are unable to maintain and promote our brand, our business and operating results may be harmed.

We believe that maintaining and promoting our brand is critical to expanding our base of users, content partners and advertisers. Maintaining and promoting our brand will depend largely on our ability to continue to provide useful, reliable and innovative products and services with a focus on a positive user experience, which we may not do successfully. We may introduce new features, products, services or terms of service that users, content partners, advertisers or platform partners do not like, which may negatively affect our brand. Additionally, the actions of content partners may affect our brand if users do not have a positive experience using third-party applications or websites integrated with Twitter or that make use of Twitter content. We will also continue to experience media, legislative or regulatory scrutiny of our decisions regarding user privacy, content and other issues, which may adversely affect our reputation and brand. For example, we previously announced our discovery of content (including some advertisements) previously displayed on our products that may be relevant to government investigations relating to Russian interference in the 2016 U.S. presidential election, which drew media and regulatory scrutiny of our actions with respect to such content. Our brand may also be negatively affected by the actions of users that are hostile or inappropriate to other people, by users impersonating other people, by users identified as spam, by use of our products or services to disseminate information that may be viewed as misleading (or intended to manipulate the opinions of our users), by users introducing excessive amounts of spam on our platform or by third parties obtaining control over users’ accounts. For example, we were recently made aware of certain actions taken by a social media marketing company to sell followers and engagement that were in the past, attackers obtained the credentials to Twitter accounts through a “phishing” attack.violation of our policies but that drew media and regulatory scrutiny on us. Maintaining and enhancing our brand may require us to make substantial investments and these investments may not achieve the desired goals. If we fail to successfully promote and maintain our brand or if we incur excessive expenses in this effort, our business and operating results could be adversely affected.

Negative publicity could adversely affect our business and operating results.

We receive a high degree of media coverage around the world. Negative publicity about our company, including about our product quality and reliability of our products or of content shared on our platform, changes to our products and services, privacy and security practices (including actions taken with respect to certain users or accounts or reports regarding government surveillance), litigation, regulatory activity, the actions of our users (including actions taken by prominent users on our platform or the dissemination of information that may be viewed as misleading or as intended to manipulate the opinions of our users) or user experience with our products and services, even if inaccurate, could adversely affect our reputation and the confidence in and the use of our products and services. Such negative publicity could also have an adverse effect on the size, engagement and loyalty of our user base and result in decreased revenue, which could adversely affect our business and operating results.

Spam could diminish the user experience on our platform, which could damage our reputation and deter our current and potential users from using our products and services.

“Spam” on Twitter refers to a range of abusive activities that are prohibited by our terms of service and is generally defined as unsolicited, repeated actions that negatively impact other users with the general goal of drawing user attention to a given account, site, product or idea. This includes posting large numbers of unsolicited mentions of a user, duplicate Tweets, malicious automation, misleading links (e.g., to malware or “click-jacking” pages) or other false or misleading content, and aggressively following and un-following accounts, adding users to lists, sending invitations, Retweeting and liking Tweets to inappropriately attract attention. Our terms of service also prohibit the creation of serial or bulk accounts, both manually or using automation, for disruptive or abusive purposes, such as to Tweet spam or to artificially inflate the popularity of users seeking to promote themselves on Twitter. Although we continue to invest resources to reduce spam on Twitter, we expect spammers will continue to seek ways to act inappropriately on our platform. In addition, we expect that increases in the number of users on our platform will result in increased efforts by spammers to misuse our platform. We continuously combat spam, including by suspending or terminating accounts we believe to be spammers and launching algorithmic changes focused on curbing abusive activities. Our actions to combat spam require the diversion of significant time and focus of our engineering team from improving our products and services. If spam increases on Twitter, this could hurt our reputation for delivering relevant content or reduce user growth and user engagement and result in continuing operational cost to us.

Action by governments to restrict access to our products and services or censor Twitter content could harm our business and operating results.

Governments have sought, and may in the future seek, to censor content available through our products and services restrict access to our products and services from their country entirely or impose other restrictions that may affect the accessibility of our products and services for an extended period of time or indefinitely. For example, domestic Internet service providers in China have blocked access to Twitter, and other countries, including Iran, Libya, Pakistan, Turkey and Syria, have intermittently restricted access to Twitter, and we believe that access to Twitter has been blocked in these countries primarily for political reasons. In addition, governments in these or other countries may seek to restrict access to our products and services based on our decisions around user content, providing user information in response to governmental requests, or other matters. In the event that access to our products and services is restricted, in whole or in part, in one or more countries or our competitors are able to successfully penetrate geographic markets that we cannot access, our ability to retain or increase our user base and user engagement may be adversely affected, and our operating results may be harmed.

Our future performance depends in part on support from our content partners and data partners.

We believe user engagement with our products and services depends in part on the availability of applications and content generated by our content or platform partners. For instance, in AprilJuly 2016, we partnered with the National FootballMajor League Baseball Advanced Media to deliver a free live digital video stream of NFL Thursday Night Footballweekly MLB baseball games on Twitter. If our content or platform partners focus their efforts on other platforms, the availability and quality of applications and content for our products and services may suffer. There is no assurance that our content or platform partners will continue to develop and maintain applications and content for our products and services. If our content or platform partners cease to develop and maintain applications and content for our products and services, user engagement may decline. In addition, we generate revenue from licensing our historical and real-time data to third parties. If any of these relationships are terminated or not renewed on economic and other terms that are acceptable to us, or if we are unable to enter into similar relationships in the future, our operating results could be adversely affected.

Our international operations are subject to increased challenges and risks.

We have offices around the world and our products and services are available in multiple languages. However, our ability to manage our business and conduct our operations internationally requires considerable management attention and resources and is subject to the particular challenges of supporting a rapidly growing business in an environment of multiple languages, cultures, customs, legal and regulatory systems, alternative dispute systems and commercial markets. Our international operations have required and will continue to require us to invest significant funds and other resources. Operating internationally subjects us to new risks and may increase risks that we currently face, including risks associated with:

If we are unable to manage the complexity of our global operations successfully, our business, financial condition and operating results could be adversely affected.

Our products and services may contain undetected software errors, which could harm our business and operating results.

Our products and services incorporate complex software and we encourage employees to quickly develop and help us launch new and innovative features. Our software, including any open source software that is incorporated into our code, has contained, and may now or in the future contain, errors, bugs or vulnerabilities. For example, in February 2016, we discovered, and corrected, a bug that affected our password recovery systems for about 24 hours. Although this issue did not expose passwords or information that could be used directly to access an account, it had the potential to expose the email address and phone number associated with a small number of accounts (less(fewer than 10,000 active accounts). Some errors in our software code may only be discovered after the product or service has been released. Errors, vulnerabilities, or other design defects within the software on which we rely may result in a negative experience for users and advertisers who use our products, delay product introductions or enhancements, result in targeting, measurement, or billing errors, compromise our ability to protect the data of our users and/or our intellectual property or lead to reductions in our ability to provide some or all of our services. For example, in December 2016, we discovered and corrected a technical error in our Android application that resulted in incorrect reporting of certain video advertisement metrics for approximately one month. Any errors, bugs or vulnerabilities discovered in our code after release could result in damage to our reputation, loss of users, loss of content or platform partners, loss of advertisers or advertising revenue or liability for damages or other relief sought in lawsuits, regulatory inquiries or other proceedings, any of which could adversely affect our business and operating results.

Our business is subject to complex and evolving U.S. and foreign laws and regulations. These laws and regulations are subject to change and uncertain interpretation, and could result in claims, changes to our business practices, monetary penalties, increased cost of operations or declines in user growth, user engagement or ad engagement, or otherwise harm our business.

We are subject to a variety of laws and regulations in the United States and abroad that involve matters central to our business, including privacy, security, rights of publicity, data protection, content regulation, intellectual property, competition, protection of minors, consumer protection, credit card processing and taxation. Many of these laws and regulations are still evolving and being tested in courts. As a result, it is possible that these laws and regulations may be interpreted and applied in a manner that is inconsistent from country to country and inconsistent with our current policies and practices and in ways that could harm our business, particularly in the new and rapidly evolving industry in which we operate. Additionally, the introduction of new products or services may subject us to additional laws and regulations.

From time to time, governments, regulators and others have expressed concerns about whether our products, services or practices compromise the privacy of users and others. While we strive to comply with applicable data protection laws and regulations, as well as our own posted privacy policies and other obligations we may have with respect to privacy and data protection, the failure or perceived failure to so comply may result, and in some cases has resulted, in inquiries and other proceedings or actions against us by governments, regulators or others. A number of proposals have recently been adopted or are currently pending before federal, state and foreign legislative and regulatory bodies that could significantly affect our business.  For example, legislation has been introduced in the California state assembly that would require social media companies doing business in California to link every user account to a human being. Moreover, foreign data protection, privacy, consumer protection, content regulation and other laws and regulations are often more restrictive than those in the United States. In particular, the European Union and its member states traditionally have taken broader views as to types of data that are subject to privacy and data protection, and have imposed greater legal obligations on companies in this regard. A number of proposals are pending before federal, state and foreign legislative and regulatory bodies that could significantly affect our business. For example, in April 2016, European legislative bodies adopted the General Data Protection Regulation, to replace European Unionor the GDPR, has been adopted and national data protection legislation effectivewill go into effect in May 2018, which2018. The GDPR also includes more stringent operational requirements for entities processing personal information and significant penalties for non-compliance, including fines of up to €20 million or 4% of total worldwide revenue.revenue, whichever is higher. Additionally, we rely on a variety of legal bases to transfer certain personal information outside of the European Economic Area, including the EU-US Privacy Shield Framework, or Privacy Shield, and EU Standard Contractual Clauses, or SCCs. Both theThe Privacy Shield is currently under review by regulatory authorities and it and the SCCs are both subject of legal challenges in European courts, and the absence of successor legal bases for continued data transfer could require us to create duplicative, and potentially expensive, information technology infrastructure and business operations in Europe or limit our ability to collect and use personal information collected in Europe. Any of these changes to EU data protection law could disrupt our business.

Further, following a referendum in June 2016 in which voters in the United Kingdom approved an exit from the EU, it is expected that the United Kingdom government will initiatehas initiated a process to leave the EU (often referred to as “Brexit”). Brexit has created uncertainty with regard to the regulation of data protection in the United Kingdom. In particular, it is unclear whether the United Kingdom will enact data protection laws or regulations designed to be consistent with the pending EU General Data Protection RegulationGDPR and how data transfers to and from the United Kingdom will be regulated.

Similarly, there have been a number of recent legislative proposals in the United States, at both the federal and state level, that wouldcould impose new obligations in areas such as privacy and liability for copyright infringement by third parties.parties such as various Congressional efforts to restrict the scope of the protections available to online platforms under Section 230 of the Communications Decency Act, and our current protections from liability for third-party content in the United States could decrease or change. The U.S. government, including the FTC and the Department of Commerce, has announced that it is reviewing the need for greater regulation for the collection of information concerning user behavior on the Internet, including regulation aimed at restricting certain online tracking and targeted advertising practices. Additionally, recent amendments to U.S. patent laws may affect the ability of companies, including us, to protect their innovations and defend against claims of patent infringement.

Additionally, we have built and made available certain commerce solutions that connect customers and retail partners and we have relationships with third parties that perform a variety of functions such as credit cardpayments processing, tokenization, vaulting, currency conversion, fraud prevention and data security audits. The laws and regulations related to e-commerce andonline payments are complex, subject to change, and vary across different jurisdictions in the United States and globally. As a result, we may be required to spend significant time, effort and expense to comply with applicable laws and regulations. Any failure or claim of our failure to comply, or any failure or claim of failure by the above-mentioned third parties to comply, could increase our costs or could result in liabilities.  Additionally, because Twitter accepts payment via credit cards and is certified as a PCI Level 1 service provider, we are subject to payment card association operating rules and certification requirements, including the Payment Card Industry Data Security Standard.

We currently allow use of our platform without the collection of extensive personal information, such as age. We may experience additional pressure to expand our collection of personal information in order to comply with new and additional regulatory demands or we may independently decide to do so. If we obtain such additional personal information, we may be subject to additional regulation.

Regulatory investigations and settlements could cause us to incur additional expenses or change our business practices in a manner materially adverse to our business.

We have been subject to regulatory investigations in the past, and expect to continue to be subject to regulatory scrutiny as our business grows and awareness of our brand increases. In March 2011, to resolve an investigation into various incidents, we entered into a settlement agreement with the FTC that, among other things, required us to establish an information security program designed to protect non-public consumer information and also requires that we obtain biennial independent security assessments. The obligations under the settlement agreement remain in effect until the later of March 2, 2031, or the date 20 years after the date, if any, on which the U.S. government or the FTC files a complaint in federal court alleging any violation of the order. We expect to continue to be the subject of regulatory inquiries, investigations and audits in the future by the FTC and other regulators around the world.

It is possible that a regulatory inquiry, investigation or audit might result in changes to our policies or practices, and may cause us to incur substantial costs or could result in reputational harm, prevent us from offering certain products, services, features or functionalities, cause us to incur substantial costs or require us to change our business practices in a manner materially adverse to our business. Violation of existing or future regulatory orders, settlements or consent decrees could subject us to substantial monetary fines and other penalties that could negatively affect our financial condition and operating results.

If our security measures are breached, or if our products and services are subject to attacks that degrade or deny the ability of users to access our products and services, our products and services may be perceived as not being secure, users and advertisers may curtail or stop using our products and services and our business and operating results could be harmed.

Our products and services involve the storage and transmission of users’ and advertisers’ information, and security breaches expose us to a risk of loss of this information, litigation, increased security costs and potential liability. We also work with third-party vendors to process credit card payments by our customers and are subject to payment card association operating rules. We and our third-party service providers experience cyber-attacks of varying degrees on a regular basis. For example, in October 2016, we experienced a service outage as a result of several distributed denial of service attacks on our domain name service provider, Dyn.

Our products operate in conjunction with, and we are dependent upon, third-party products and components across a broad ecosystem. Additionally, the natural sunsetting of third-party products and operating systems that we use requires that our infrastructure teams reallocate time and attention to migration and updates, during which period potential security vulnerabilities could be exploited. If there is a security vulnerability (such as the recently-announced Spectre and Meltdown vulnerabilities) in one of these components and if there is a security exploit targeting it, we could face increased costs, liability claims, reduced revenue, or harm to our reputation or competitive position.  

Third parties may also gain access to Twitter user names and passwords without attacking Twitter directly by combining credential information from other recent breaches, using malware on victim machines that are stealing passwords for all sites, or a combination of both.  In addition, some of our developers or other partners, such as third partythird-party applications to which our users have given permission to Tweet on their behalf, may receive or store information provided by us or by our users through mobile or web applications integrated with us. If these third parties or developers fail to adopt or adhere to adequate data security practices, or in the event of a breach of their networks, our data or our users' data may be improperly accessed, used, or disclosed.

As a result, unauthorized parties have obtained, and may in the future obtain, access to our data or our users’ or advertisers’ data. For example, we have previously disclosed that sophisticated unknown third parties had attacked our systems and may have had access to limited information for small subset of our users. In addition, a breach of a third-party application that has been trusted by a user could result in the account issuing Tweets, Likes, Retweets, or Direct Messages without such user’s knowledge or consent. Any systems failure or actual or perceived compromise of our security that results in the unauthorized access to or release of our users’ or advertisers’ data, such as credit card data, could significantly limit the adoption of our products and services, as well as harm our reputation and brand and, therefore, our business.

Our security measures may also be breached due to employee error, malfeasance or otherwise. Additionally, outside parties may attempt to fraudulently induce employees, users or advertisers to disclose sensitive information in order to gain access to our data or our users’ or advertisers’ data or accounts, or may otherwise obtain access to such data or accounts. Since our users and advertisers may use their Twitter accounts to establish and maintain online identities, unauthorized communications from Twitter accounts that have been compromised may damage their reputations and brands as well as ours. Because the techniques used to obtain unauthorized access, disable or degrade service or sabotage systems change frequently and often are not recognized until launched against a target, we may be unable to anticipate these techniques or to implement adequate preventative measures. If an actual or perceived breach of our security occurs, the market perception of the effectiveness of our security measures could be harmed, our users and advertisers may be harmed, lose trust and confidence in us, decrease the use of our products and services or stop using our products and services in their entirety. We may also incur significant legal and financial exposure, including legal claims, higher transaction fees and regulatory fines and penalties. Any of these actions could have a material and adverse effect on our business, reputation and operating results.

We may face lawsuits or incur liability as a result of content published or made available through our products and services.

We have faced and will continue to face claims relating to content that is published or made available through our products and services or third partythird-party products or services. In particular, the nature of our business exposes us to claims related to defamation, intellectual property rights, rights of publicity and privacy, illegal content, misinformation, content regulation and personal injury torts. The laws relating to the liability of providers of online products or services for activities of their users remains somewhat unsettled, both within the United States and internationally. This risk may be enhanced in certain jurisdictions outside the United States where we may be less protected under local laws than we are in the United States. For example, we are subject to recently enacted legislation in Germany that may impose significant fines for failure to comply with certain content removal and disclosure obligations. In addition, the public nature of communications on our network exposes us to risks arising from the creation of impersonation accounts intended to be attributed to our users or advertisers. We could incur significant costs investigating and defending these claims. If we incur material costs or liability as a result of these occurrences, our business, financial condition and operating results could be adversely affected.

Our intellectual property rights are valuable, and any inability to protect them could reduce the value of our products, services and brand.

Our trade secrets, trademarks, copyrights, patents and other intellectual property rights are important assets. We rely on, and expect to continue to rely on, a combination of confidentiality and license agreements with our employees, consultants and third parties with whom we have relationships, as well as trademark, trade dress, domain name, copyright, trade secret and patent laws, to protect our brand and other intellectual property rights. However, various events outside of our control pose a threat to our intellectual property rights, as well as to our products, services and technologies. For example, we may fail to obtain effective intellectual property protection, or effective intellectual property protection may not be available in every country in which our products and services are available. Also, the efforts we have taken to protect our intellectual property rights may not be sufficient or effective, and any of our intellectual property rights may be challenged, which could result in them being narrowed in scope or declared invalid or unenforceable. There can be no assurance our intellectual property rights will be sufficient to protect against others offering products or services that are substantially similar to ours and compete with our business.

We rely on non-patented proprietary information and technology, such as trade secrets, confidential information, know-how and technical information. While in certain cases we have agreements in place with employees and third parties that place restrictions on the use and disclosure of this intellectual property, these agreements may be breached, or this intellectual property may otherwise be disclosed or become known to our competitors, which could cause us to lose any competitive advantage resulting from this intellectual property.

We are pursuing registration of trademarks and domain names in the United States and in certain jurisdictions outside of the United States. Effective protection of trademarks and domain names is expensive and difficult to maintain, both in terms of application and registration costs as well as the costs of defending and enforcing those rights. We may be required to protect our rights in an increasing number of countries, a process that is expensive and may not be successful or which we may not pursue in every country in which our products and services are distributed or made available.

We are party to numerous agreements that grant licenses to third parties to use our intellectual property, including our trademarks. For example, many third parties distribute their content through Twitter, or embed Twitter content in their applications or on their websites, and make use of our trademarks in connection with their services. If the licensees of our trademarks are not using our trademarks properly, it may limit our ability to protect our trademarks and could ultimately result in our trademarks being declared invalid or unenforceable. We have a policy designed to assist third parties in the proper use of our brand, trademarks and other assets, and we have an internal team dedicated to enforcing our policy and protecting our brand. Our brand protection team routinely receives and reviews reports of improper and unauthorized use of the Twitter brand, trademarks or assets and issues takedown notices or initiates discussions with the third parties to correct the issues. However, there can be no assurance that we will be able to protect against the unauthorized use of our brand, trademarks or other assets. If we fail to maintain and enforce our trademark rights, the value of our brand could be diminished. There is also a risk that one or more of our trademarks could become generic, which could result in them being declared invalid or unenforceable. For example, there is a risk that the word “Tweet” could become so commonly used that it becomes synonymous with any short comment posted publicly on the Internet, and if this happens, we could lose protection of this trademark.

We also seek to obtain patent protection for some of our technology and as of December 31, 2016, we had 1,023 issued U.S. patents.technology. We may be unable to obtain patent protection for our technologies, and our existing patents, and any patents that may be issued in the future, may not provide us with competitive advantages or distinguish our products and services from those of our competitors. In addition, any patents may be contested, circumvented, or found unenforceable or invalid, and we may not be able to prevent third parties from infringing or otherwise violating them. Effective protection of patent rights is expensive and difficult to maintain, both in terms of application and maintenance costs, as well as the costs of defending and enforcing those rights.

Our Innovator’s Patent Agreement, or IPA, also limitscan limit our ability to prevent infringement of our patents. In May 2013, we implemented the IPA, which we enter into with our employees and consultants, including our founders. The IPA, which applies to our current and future patents, allows us to assert our patents defensively. The IPA also allows us to assert our patents offensively with the permission of the inventors of the applicable patent. Under the IPA, an assertion of claims is considered for a defensive purpose if the claims are asserted: (i) against an entity that has filed, maintained, threatened or voluntarily participated in a patent infringement lawsuit against us or any of our users, affiliates, customers, suppliers or distributors; (ii) against an entity that has used its patents offensively against any other party in the past ten years, so long as the entity has not instituted the patent infringement lawsuit defensively in response to a patent litigation threat against the entity; or (iii) otherwise to deter a patent litigation threat against us or our users, affiliates, customers, suppliers or distributors. In addition, the IPA provides that the above limitations apply to any future owner or exclusive licensee of any of our patents, which could limit our ability to sell or license our patents to third parties. While we may be able to claim protection of our intellectual property under other rights, such as trade secrets or contractual obligations with our employees not to disclose or use confidential information, we may be unable to assert our patent rights against third parties that we believe are infringing our patents, even if such third parties are developing products and services that compete with our products and services. For example, in the event that an inventor of one of our patents leaves us for another company and uses our patented technology to compete with us, we would not be able to assert that patent against such other company unless the assertion of the patent right is for a defensive purpose. In such event, we may be limited in our ability to assert a patent right against another company, and instead would need to rely on trade secret protection or the contractual obligation of the inventor to us not to disclose or use our confidential information. In addition, the terms of the IPA could affect our ability to monetize our intellectual property portfolio.

Significant impairments of our intellectual property rights, and limitations on our ability to assert our intellectual property rights against others, could harm our business and our ability to compete.

Also, obtaining, maintaining and enforcing our intellectual property rights is costly and time consuming. Any increase in the unauthorized use of our intellectual property could make it more expensive to do business and harm our operating results.

We are currently, and expect to be in the future, party to intellectual property rights claims that are expensive and time consuming to defend, and, if resolved adversely, could have a significant impact on our business, financial condition or operating results.

Companies in the internet, technology and media industries are subject to litigation based on allegations of infringement, misappropriation or other violations of intellectual property or other rights. Many companies in these industries, including many of our competitors, have substantially larger patent and intellectual property portfolios than we do, which could make us a target for litigation as we may not be able to assert counterclaims against parties that sue us for patent, or other intellectual property infringement. In addition, various “non-practicing entities” that own patents and other intellectual property rights often attempt to assert claims in order to extract value from technology companies. From time to time we receive claims from third parties which allege that we have infringed upon their intellectual property rights. Further, from time to time we may introduce new products, product features and services, including in areas where we currently do not have an offering, which could increase our exposure to patent and other intellectual property claims from competitors and non-practicing entities. In addition, although our standard terms and conditions for our Promoted Products and public APIs do not provide advertisers and platform partners with indemnification for intellectual property claims against them, some of our agreements with advertisers, content partners, platform partners and data partners require us to indemnify them for certain intellectual property claims against them, which could require us to incur considerable costs in defending such claims, and may require us to pay significant damages in the event of an adverse ruling. Such advertisers, content partners, platform partners and data partners may also discontinue use of our products, services and technologies as a result of injunctions or otherwise, which could result in loss of revenue and adversely impact our business.

We presently are involved in a number of intellectual property lawsuits, and as we face increasing competition and gain an increasingly high profile and develop new products, we expect the number of patent and other intellectual property claims against us to grow. There may be intellectual property or other rights held by others, including issued or pending patents, that cover significant aspects of our products and services, and we cannot be sure that we are not infringing or violating, and have not infringed or violated, any third-party intellectual property rights or that we will not be held to have done so or be accused of doing so in the future. Any claim or litigation alleging that we have infringed or otherwise violated intellectual property or other rights of third parties, with or without merit, and whether or not settled out of court or determined in our favor, could be time-consuming and costly to address and resolve, and could divert the time and attention of our management and technical personnel. Some of our competitors have substantially greater resources than we do and are able to sustain the costs of complex intellectual property litigation to a greater degree and for longer periods of time than we could. The outcome of any litigation is inherently uncertain, and there can be no assurances that favorable final outcomes will be obtained in all cases. In addition, plaintiffs may seek, and we may become subject to, preliminary or provisional rulings in the course of any such litigation, including potential preliminary injunctions requiring us to cease some or all of our operations. We may decide to settle such lawsuits and disputes on terms that are unfavorable to us. Similarly, if any litigation to which we are a party is resolved adversely, we may be subject to an unfavorable judgment that may not be reversed upon appeal. The terms of such a settlement or judgment may require us to cease some or all of our operations or pay substantial amounts to the other party. In addition, we may have to seek a license to continue practices found to be in violation of a third-party’s rights. If we are required, or choose to enter into royalty or licensing arrangements, such arrangements may not be available on reasonable terms, or at all, and may significantly increase our operating costs and expenses. As a result, we may also be required to develop or procure alternative non-infringing technology, which could require significant effort and expense or discontinue use of the technology. An unfavorable resolution of the disputes and litigation referred to above could adversely affect our business, financial condition and operating results.

Many of our products and services contain open source software, and we license some of our software through open source projects, which may pose particular risks to our proprietary software, products, and services in a manner that could have a negative effect on our business.

We use open source software in our products and services and will use open source software in the future. In addition, we regularly contribute software source code to open source projects under open source licenses or release internal software projects under open source licenses, and anticipate doing so in the future. The terms of many open source licenses to which we are subject have not been interpreted by U.S. or foreign courts, and there is a risk that open source software licenses could be construed in a manner that imposes unanticipated conditions or restrictions on our ability to provide or distribute our products or services. Additionally, we may from time to time face claims from third parties claiming ownership of, or demanding release of, the open source software or derivative works that we developed using such software, which could include our proprietary source code, or otherwise seeking to enforce the terms of the applicable open source license. These claims could result in litigation and could require us to make our software source code freely available, purchase a costly license or cease offering the implicated products or services unless and until we can re-engineer them to avoid infringement. This re-engineering process could require significant additional research and development resources, and we may not be able to complete it successfully. In addition to risks related to license requirements, use of certain open source software may pose greater risks than use of third-party commercial software, as open source licensors generally do not provide warranties or controls on the origin of software. Any of these risks could be difficult to eliminate or manage, and, if not addressed, could have a negative effect on our business, financial condition and operating results.

We may require additional capital to support our operations or the growth of our business, and we cannot be certain that this capital will be available on reasonable terms when required, or at all.

From time to time, we may need additional financing to operate or grow our business. Our ability to obtain additional financing, if and when required, will depend on investor and lender demand, our operating performance, the condition of the capital markets and other factors, and we cannot assure you that additional financing will be available to us on favorable terms when required, or at all. If we raise additional funds through the issuance of equity, equity-linked or debt securities, those securities may have rights, preferences or privileges senior to the rights of our common stock, and our existing stockholders may experience dilution. If we are unable to obtain adequate financing or financing on terms satisfactory to us when we require it, our ability to continue to support the operation or growth of our business could be significantly impaired and our operating results may be harmed.

We rely on assumptions and estimates to calculate certain of our key metrics, and real or perceived inaccuracies in such metrics may harm our reputation and negatively affect our business.

The number of our active users is calculated using internal company data that has not been independently verified. While these numbers are based on what we believe to be reasonable calculations for the applicable period of measurement, there are inherent challenges in measuring usage and user engagement across our large user base around the world. For example, there are a number of false or spam accounts in existence on our platform. We estimate that false or spam accounts represent lessfewer than 5% of our MAUs as of December 31, 2016.2017. However, this estimate is based on an internal review of a sample of accounts and we apply significant judgment in making this determination. As such, our estimation of false or spam accounts may not accurately represent the actual number of such accounts, and the actual number of false or spam accounts could be higher than we have currently estimated. We are continually seeking to improve our ability to estimate the total number of spam accounts and eliminate them from the calculation of our active users, but we otherwise treat multiple accounts held by a single person or organization as multiple users for purposes of calculating our active users because we permit people and organizations to have more than one account. Additionally, some accounts used by organizations are used by many people within the organization. As such, the calculations of our active users may not accurately reflect the actual number of people or organizations using our platform.Further, we rely on third-party SMS aggregators and mobile carriers to deliver SMS messages to certain of our users. If, however, we are notified of material deliverability issues because of, for example, infrastructure issues at the service-provider level or governmental restrictions based on content, we do not include the affected users in MAUs. We may also discover unexpected errors in our internal data that resulted from technical or other errors. For example, in the third quarter of 2017, we discovered that since the fourth quarter of 2014 we had included users of certain third-party applications as Twitter MAUs that should not have been considered MAUs. These third-party applications used Digits, a software development kit of our now-divested Fabric platform that allowed third-party applications to send authentication messages via SMS through our systems, which did not relate to activity on the Twitter platform. Although the change in the MAUs was relatively small in relation to our overall MAU numbers, we may face increased scrutiny as a result of the error.

Our metrics are also affected by mobile applications that automatically contact our servers for regular updates with no discernable user-initiated action involved, and this activity can cause our system to count the user associated with such a device as an active user on the day such contact occurs. The calculations of MAUs and DAUs presented in this Annual Report on Form 10-K may be affected by this activity. The impact of this automatic activity on our metrics varies by geography because mobile application usage varies in different regions of the world. In addition, our data regarding user geographic location is based on the IP address or phone number associated with the account when a user initially registered the account on Twitter. That IP address or phone number may not always accurately reflect a user’s actual location at the time of such user’s engagement on our platform.

We regularly review and may adjust our processes for calculating our internal metrics to improve their accuracy. We present and discuss ourOur total audience metrics are based on both internal metrics and data from Google Analytics, which measures unique visitors to our properties. Our measures of user growth and user engagement may differ from estimates published by third parties or from similarly-titled metrics of our competitors due to differences in methodology. If advertisers, content or platform partners or investors do not perceive our user metrics to be accurate representations of our user base or user engagement, or if we discover material inaccuracies in our user metrics, our reputation may be harmed and content partners, advertisers and platform partners may be less willing to allocate their budgets or resources to our products and services, which could negatively affect our business and operating results. Further, as our business develops, we may revise or cease reporting metrics if we determine that such metrics are no longer accurate or appropriate measures of our performance. For example, we stopped disclosing timeline views as we no longer believed that metric was helpful in measuring engagement on our platform. If investors, analysts or customers do not believe our reported measures of user engagement are sufficient or accurately reflect our business, we may receive negative publicity and our operating results may be harmed.

Spam could diminish the user experience on our platform, which could damage our reputation and deter our current and potential users from using our products and services.

“Spam” on Twitter refers to a range of abusive activities that are prohibited by our terms of service and is generally defined as unsolicited, repeated actions that negatively impact other users with the general goal of drawing user attention to a given account, site, product or idea. This includes posting large numbers of unsolicited mentions of a user, duplicate Tweets, misleading links (e.g., to malware or “click-jacking” pages) or other false or misleading content, and aggressively following and un-following accounts, adding users to lists, sending invitations, Retweeting and liking Tweets to inappropriately attract attention. Our terms of service also prohibit the creation of serial or bulk accounts, both manually or using automation, for disruptive or abusive purposes, such as to tweet spam or to artificially inflate the popularity of users seeking to promote themselves on Twitter. Although we continue to invest resources to reduce spam on Twitter, we expect spammers will continue to seek ways to act inappropriately on our platform. In addition, we expect that increases in the number of users on our platform will result in increased efforts by spammers to misuse our platform. We continuously combat spam, including by suspending or terminating accounts we believe to be spammers and launching algorithmic changes focused on curbing abusive activities. Our actions to combat spam require the diversion of significant time and focus of our engineering team from improving our products and services. If spam increases on Twitter, this could hurt our reputation for delivering relevant content or reduce user growth and user engagement and result in continuing operational cost to us.

We rely in part on application marketplaces and Internet search engines to drive traffic to our products and services, and if we fail to appear high up in the search results or rankings, traffic to our platform could decline and our business and operating results could be adversely affected.

We rely on application marketplaces, such as Apple’s App Store and Google’s Play, to drive downloads of our mobile applications. In the future, Apple, Google or other operators of application marketplaces may make changes to their marketplaces which make access to our products and services more difficult or limit our use of data to provide targeted advertising. We also depend in part on Internet search engines, such as Google, Apple Spotlight, Bing and Yahoo, to drive traffic to our website. For example, when a user types an inquiry into a search engine, we rely on a high organic search result ranking of our webpages in these search results to refer the user to our website. However, our ability to maintain high organic search result rankings is not within our control. Our competitors’ search engine optimization, or SEO, efforts may result in their websites receiving a higher search result page ranking than ours, or Internet search engines could revise their methodologies in a way that would adversely affect our search result rankings. If Internet search engines modify their search algorithms in ways that are detrimental to us, or if our competitors’ SEO efforts are more successful than ours, the growth in our user base could slow. Our website has experienced fluctuations in search result rankings in the past, and we anticipate similar fluctuations in the future. Any reduction in the number of users directed to our mobile applications or website through application marketplaces and search engines could harm our business and operating results.

More people are using devices other than personal computers to access the Internet and new platforms to produce and consume content, and we need to continue to promote the adoption of our mobile applications, and our business and operating results may be harmed if we are unable to do so.

The number of people who access the Internet through devices other than personal computers, including mobile phones, tablets, video game consoles and television set-top devices, has increased dramatically in the past few years. In the three months ended December 31, 2016, 89%2017, 93% of our advertising revenue was generated from mobile devices. Since we generate a majority of our advertising revenue through users on mobile devices, we must continue to drive adoption of our mobile applications. However, in emerging markets like India and Pakistan, a significant portion of users use feature phones and communicate via SMS messaging, both of which have limited functionality and neither of which may be able to take full advantage of our products and services offered on smartphone or our website or desktop applications. In addition, mobile users frequently change or upgrade their mobile devices. Our business and operating results may be harmed if our users do not install our mobile application when they change or upgrade their mobile device. Although we generate the majority of our advertising revenue from ad engagements on mobile devices, certain of our products and services, including Promoted Trends and Promoted Accounts, receive less prominence on our mobile applications than they do on our desktop applications. This has in the past reduced, and may in the future continue to reduce, the amount of revenue we are able to generate from these products and services as users increasingly access our products and services through mobile and alternative devices. In addition, as new devices and platforms are continually being released, users may consume content in a manner that is more difficult to monetize. If we are unable to develop products and services that are compatible with new devices and platforms, or if we are unable to drive continued adoption of our mobile applications, our business and operating results may be harmed.

Acquisitions, divestitures and investments could disrupt our business and harm our financial condition and operating results.

Our success will depend, in part, on our ability to expand our products, product features and services, and grow our business in response to changing technologies, user and advertiser demands, and competitive pressures. In some circumstances, we may determine to do so through the acquisition of complementary businesses and technologies rather than through internal development, including, for example, our acquisitions of Periscope, a live-streaming video mobile application, and MoPub, a mobile-focused advertising exchange; and TellApart, Inc., a marketing technology company providing retailers and e-commerce advertisers with unique retargeting capabilities.exchange. The identification of suitable acquisition candidates can be difficult, time-consuming and costly, and we may not be able to successfully complete identified acquisitions. The risks we face in connection with acquisitions include:

Our failure to address these risks or other problems encountered in connection with our past or future acquisitions and investments could cause us to fail to realize the anticipated benefits of these acquisitions or investments, cause us to incur unanticipated liabilities, and harm our business generally. Future acquisitions could also result in dilutive issuances of our equity securities, the incurrence of debt, contingent liabilities, amortization expenses, incremental operating expenses or the impairment of goodwill, any of which could harm our financial condition or operating results.

We also make investments in privately-held companies in furtherance of our strategic objectives. We may not realize a return and may recognize a loss on such investments. Many of the instruments in which we invest are non-marketable at the time of our initial investment. Companies in which we invest range from early-stage companies still defining their strategic direction to more mature companies with established revenue streams and business models. The success of our investment in any company is typically dependent on the availability to the company of additional funding on favorable terms, or a liquidity event, such as a public offering or acquisition. If any of the companies in which we invest decrease in value, we could lose all or part of our investment. For example, in the year ended December 31, 2017, we recorded a $62.4 million cost-method investment impairment charge relating to an investment in a privately-held company.

In certain cases, we have also divested or stopped investing in certain products. For instance, in January 2017, we divested certain assets related to our Fabric platform. In 2017, we also deprecated certain of our revenue products, including TellApart, which was acquired in 2015. In these cases, we have needed to and may, in the future, need to restructure operations, terminate employees and/or incur other expenses. We may not realize the expected benefits and cost savings of these actions and our results may be harmed.

If we fail to maintain an effective system of disclosure controls and internal control over financial reporting, our ability to produce timely and accurate financial statements or comply with applicable regulations could be impaired.

As a public company, we are subject to the reporting requirements of the Securities Exchange Act of 1934, as amended, or the Exchange Act, the Sarbanes-Oxley Act of 2002, as amended, or the Sarbanes-Oxley Act, and the listing standards of the New York Stock Exchange. The Sarbanes-Oxley Act requires, among other things, that we maintain effective disclosure controls and procedures and internal control over financial reporting. In order to maintain and improve the effectiveness of our disclosure controls and procedures and internal control over financial reporting, we have expended, and anticipate that we will continue to expend, significant resources, including accounting-related costs and significant management oversight.

Any failure to develop or maintain effective controls, or any difficulties encountered in their implementation or improvement, could cause us to be subject to one or more investigations or enforcement actions by state or federal regulatory agencies, stockholder lawsuits or other adverse actions requiring us to incur defense costs, pay fines, settlements or judgments. Any such failures could also cause investors to lose confidence in our reported financial and other information, which would likely have a negative effect on the trading price of our common stock. In addition, if we are unable to continue to meet these requirements, we may not be able to remain listed on the New York Stock Exchange.

If currency exchange rates fluctuate substantially in the future, our operating results, which are reported in U.S. dollars, could be adversely affected.

Our international operations expose us to the effects of fluctuations in currency exchange rates. We incur expenses for employee compensation and other operating expenses at our international locations in the local currency, and accept payment from advertisers or data partners in currencies other than the U.S. dollar. Since we conduct business in currencies other than U.S. dollars but report our operating results in U.S. dollars, we face exposure to fluctuations in currency exchange rates. While we enter into foreign currency forward contracts with financial institutions to reduce the risk that our earnings may be adversely affected by the impact of exchange rate fluctuations on monetary assets or liabilities denominated in currencies other than the functional currency of a subsidiary, exchange rate fluctuations between the U.S. dollar and other currencies could have a material impact on our operating results.

Servicing our convertible senior notes may require a significant amount of cash, and we may not have sufficient cash flow or the ability to raise the funds necessary to satisfy our obligations under such notes, and our future debt may contain limitations on our ability to pay cash upon conversion or repurchase of such notes.

In 2014, we issued $935.0 million in aggregate principal amount of 0.25% convertible senior notes due 2019, or the 2019 Notes, and $954.0 million in aggregate principal amount of 1.00% convertible senior notes due 2021, or the 2021 Notes and together with the 2019 Notes, the Notes, in private placements to qualified institutional buyers. As of December 31, 2016,2017, we had a total par value of $1.89 billion of outstanding Notes.

Holders of the Notes will have the right under the indenture for the Notes to require us to repurchase all or a portion of their notes upon the occurrence of a fundamental change before the relevant maturity date, in each case at a repurchase price equal to 100% of the principal amount of the Notes, plus accrued and unpaid interest, if any, to the fundamental change repurchase date. In addition, upon conversion of the Notes, unless we elect to deliver solely shares of our common stock to settle such conversion (other than paying cash in lieu of delivering any fractional shares), we will be required to make cash payments in respect of the Notes being converted. Moreover, we will be required to repay the notes in cash at their maturity, unless earlier converted or repurchased.

Our ability to refinance the Notes, make cash payments in connection with conversions of the Notes or repurchase the Notes in the event of a fundamental change will depend on market conditions and our future performance, which is subject to economic, financial, competitive and other factors beyond our control. We also may not use the cash we have raised through the issuance of the Notes in an optimally productive and profitable manner. However, since inception we have incurred significant operating losses and we historically had not been cash flow positive and may not be in the future. As a result, we may not have enough available cash or be able to obtain financing on commercially reasonable terms or at all, at the time we are required to make repurchases of notes surrendered therefor or pay cash with respect to notes being converted or at their maturity and our level of indebtedness could adversely affect our future operations by increasing our vulnerability to adverse changes in general economic and industry conditions and by limiting or prohibiting our ability to obtain additional financing for future capital expenditures, acquisitions and general corporate and other purposes. In addition, if we are unable to make cash payments upon conversion of the Notes we would be required to issue significant amounts of our common stock, which would be dilutive to existing stockholders. If we do not have sufficient cash to repurchase the Notes following a fundamental change, we would be in default under the terms of the Notes, which could seriously harm our business. In addition, the terms of the Notes do not limit the amount of future indebtedness we may incur. If we incur significantly more debt, this could intensify the risks described above.

Our business is subject to the risks of earthquakes, fire, power outages, floods and other catastrophic events, and to interruption by man-made problems such as terrorism.

A significant natural disaster, such as an earthquake, fire, flood or significant power outage could have a material adverse impact on our business, operating results, and financial condition. Our headquarters and certain of our co-located data center facilities are located in the San Francisco Bay Area, a region known for seismic activity. Despite any precautions we may take, the occurrence of a natural disaster or other unanticipated problems at our data centers could result in lengthy interruptions in our services. In addition, acts of terrorism and other geo-political unrest could cause disruptions in our business. All of the aforementioned risks may be further increased if our disaster recovery plans prove to be inadequate. We have implemented a disaster recovery program, which allows us to move production to a back-up data center in the event of a catastrophe. Although this program is functional, we do not currently serve network traffic equally from each data center, so if our primary data center shuts down, there will be a period of time that our products or services, or certain of our products or services, will remain inaccessible to our users or our users may experience severe issues accessing our products and services.

We do not carry business interruption insurance sufficient to compensate us for the potentially significant losses, including the potential harm to our business that may result from interruptions in our ability to provide our products and services.

We may have exposure to greater than anticipated tax liabilities, which could adversely impact our operating results.

Our income tax obligations are based in part on our corporate operating structure, including the manner in which we develop, value and use our intellectual property and the scope of our international operations. The tax laws applicable to our international business activities, including the laws of the United States and other jurisdictions, are subject to interpretation. The taxing authorities of the jurisdictions in which we operate may challenge our methodologies for valuing developed technology (or other intangible assets) or intercompany arrangements, which could increase our worldwide effective tax rate and harm our financial condition and operating results. On October 5, 2015, the Organization for Economic Cooperation and Development (OECD), an international association of thirty four countries, including the U.S. and UK, released the final reports from its Base Erosion and Profit Shifting (BEPS) Action Plans. The BEPS recommendations covered a number of issues, including country-by-country reporting, permanent establishment rules, transfer pricing rules and tax treaties. Future tax reform resulting from this development may result in changes to long-standing tax principles, which could adversely affect our effective tax rate or result in higher cash tax liabilities. We are subject to review and audit by U.S. federal and state and foreign tax authorities. Tax authorities may disagree with certain positions we have taken and any adverse outcome of such a review or audit could have a negative effect on our financial position and operating results. In addition, our future income taxes could be adversely affected by earnings being lower than anticipated in jurisdictions that have lower statutory tax rates and higher than anticipated in jurisdictions that have higher statutory tax rates, by changes in the valuation of our deferred tax assets and liabilities, or by changes in tax laws, regulations or accounting principles, as well as certain discrete items. The 2017 Tax Cuts and Jobs Act (the “Tax Act”) contains many significant changes to the U.S. federal income tax laws, the consequences to us of which have not yet been fully determined and which could have a material impact on the value of our deferred tax assets, could result in significant one-time charges in the current or future taxable years, and could increase our future U.S. tax expense. Furthermore, changes to the taxation of undistributed foreign earnings could change our future intentions regarding reinvestment of such earnings. Greater than anticipated tax expenses, or disputes with tax authorities, could adversely impact our operating results.

Uncertainties in the interpretation and application of the 2017 Tax Cuts and Jobs Act could materially affect our tax obligations and effective tax rate.

The recently-enacted Tax Act significantly affected U.S. tax law by changing how U.S. income tax is assessed on multinational corporations. The Tax Act requires complex computations not previously provided for in U.S. tax law and the U.S. Department of Treasury may issue regulations and interpretive guidance that may significantly impact how we will apply the law and impact our results of operations.  Additionally, the application of accounting guidance for such items is currently uncertain. Further, compliance with the Tax Act and the accounting for such provisions call for the collection and preparation of information not previously required. Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Act, we have made reasonable estimates and recorded a provisional estimate of the effect of the Tax Act in our financial statements for the year ended December 31, 2017. As additional regulatory and interpretive guidance is issued, we may refine our analysis and make adjustments that differ from our current provisional amounts, which could materially affect our tax obligations and effective tax rate.

If our goodwill or intangible assets become impaired, we may be required to record a significant charge to earnings.

Under generally accepted accounting principles in the United States, or GAAP, we review our intangible assets for impairment when events or changes in circumstances indicate the carrying value may not be recoverable. Goodwill is required to be tested for impairment at least annually. As of December 31, 2016,2017, we had recorded a total of $1.28$1.24 billion of goodwill and intangible assets. An adverse change in market conditions or financial results, particularly if such change has the effect of changing one of our critical assumptions or estimates, could result in a change to the estimation of fair value that could result in an impairment charge to our goodwill or intangible assets. Any such material charges may have a material negative impact on our operating results.

Our ability to use our net operating loss carryforwards and certain other tax attributes may be limited.

As of December 31, 2016,2017, we had U.S. federal net operating loss carryforwards of approximately $3.47$3.43 billion and state net operating loss carryforwards of approximately $1.41$1.47 billion. Under Sections 382 and 383 of the Internal Revenue Code of 1986, as amended, or the Code, if a corporation undergoes an “ownership change,” the corporation’s ability to use its pre-change net operating loss carryforwards and other pre-change tax attributes, such as research tax credits, to offset its post-change income and taxes may be limited. In general, an “ownership change” occurs if there is a cumulative change in our ownership by “5% shareholders” that exceeds 50 percentage points over a rolling three-year period. Similar rules may apply under state tax laws. In the event that it is determined that we have in the past experienced an ownership change, or if we experience one or more ownership changes as a result of future transactions in our stock, then we may be limited in our ability to use our net operating loss carryforwards and other tax assets to reduce taxes owed on the net taxable income that we earn. In addition, the Tax Act includes changes to the U.S. federal corporate income tax rate, and our net operating loss carryforwards and other deferred tax assets have been revalued at the newly enacted rate. We do not expect this to have a material impact on our financials because we currently maintain a full valuation allowance on our U.S. deferred tax assets. Any such limitations on the ability to use our net operating loss carryforwards and other tax assets could adversely impact our business, financial condition and operating results.

Risks Related to Ownership of Our Common Stock

Anti-takeover provisions contained in our amended and restated certificate of incorporation and amended and restated bylaws, as well as provisions of Delaware law, could impair a takeover attempt.

Our amended and restated certificate of incorporation, amended and restated bylaws and Delaware law contain provisions which could have the effect of rendering more difficult, delaying, or preventing an acquisition deemed undesirable by our board of directors. Among other things, our amended and restated certificate of incorporation and amended and restated bylaws include provisions:

These provisions, alone or together, could delay or prevent hostile takeovers and changes in control or changes in our management.

As a Delaware corporation, we are also subject to provisions of Delaware law, including Section 203 of the Delaware General Corporation law, which prevents certain stockholders holding more than 15% of our outstanding common stock from engaging in certain business combinations without approval of the holders of at least two-thirds of our outstanding common stock not held by such 15% or greater stockholder.

Any provision of our amended and restated certificate of incorporation, amended and restated bylaws or Delaware law that has the effect of delaying, preventing or deterring a change in control could limit the opportunity for our stockholders to receive a premium for their shares of our common stock, and could also affect the price that some investors are willing to pay for our common stock.

The market price of our common stock has been and will likely continue to be volatile, and you could lose all or part of your investment.

The market price of our common stock has been and may continue to be highly volatile in response to various factors, some of which are beyond our control. Since shares of our common stock were sold in our initial public offering in November 2013 at a price of $26.00 per share, the reported high and low sales prices of our common stock has ranged from $74.73 to $13.72, through December 31, 2016.2017. In addition to the factors discussed in this “Risk Factors” section and elsewhere in this Annual Report on Form 10-K, factors that could cause fluctuations in the market price of our common stock include the following:

In addition, in the past, following periods of volatility in the overall market and the market price of a particular company’s securities, securities class action litigation has often been instituted against these companies. Any securities litigation can result in substantial costs and a diversion of our management’s attention and resources. We are currently subject to securities litigation and may experience more such litigation following any future periods of volatility.

The note hedge and warrant transactions may affect the value of our common stock.

Concurrently with the issuance of the Notes, we entered into note hedge transactions with certain financial institutions, which we refer to as the option counterparties. The note hedge transactions are generally expected to reduce the potential dilution upon any conversion of the Notes and/or offset any cash payments we are required to make in excess of the principal amount of converted Notes, as the case may be. We also entered into warrant transactions with the option counterparties. However, the warrant transactions could separately have a dilutive effect to the extent that the market price per share of our common stock exceeds the applicable strike price of the warrants.

The option counterparties or their respective affiliates may modify their initial hedge positions by entering into or unwinding various derivatives contracts with respect to our common stock and/or purchasing or selling our common stock or other securities of ours in secondary market transactions prior to the maturity of the Notes (and are likely to do so during any observation period related to a conversion of Notes or following any repurchase of Notes by us on any fundamental change repurchase date or otherwise). This activity could cause or avoid an increase or a decrease in the market price of our common stock.

In addition, if any such convertible note hedge and warrant transactions fail to become effective, the option counterparties or their respective affiliates may unwind their hedge positions with respect to our common stock, which could adversely affect the value of our common stock.

If securities or industry analysts do not publish or cease publishing research or reports about us, our business or our market, or if they change their recommendations regarding our common stock adversely, the price of our common stock and trading volume could decline.

The trading market for our common stock is influenced, to some extent, by the research and reports that securities or industry analysts publish about us, our business, our industry, our market or our competitors. If any of the analysts who cover us change their recommendation regarding our common stock adversely, or provide more favorable relative recommendations about our competitors, the price of our common stock would likely decline. If any analysts who cover us were to cease coverage of our company or fail to regularly publish reports on us, we could lose visibility in the financial markets, which in turn could cause the price of our common stock or trading volume to decline.

We do not expect to declare any dividends in the foreseeable future.

We do not anticipate declaring any cash dividends to holders of our common stock in the foreseeable future. In addition, our credit facility contains restrictions on payments including payments of cash dividends. Consequently, investors may need to rely on sales of our common stock after price appreciation, which may never occur, as the only way to realize any future gains on their investment.

Item 1B. UNRESOLVED STAFF COMMENTS

None.

Item 2. PROPERTIES

Facilities

As of December 31, 2016,2017, we leased office facilities around the world totaling approximately 1,599,0001,572,000 square feet, including approximately 760,000749,000 square feet for our corporate headquarters in San Francisco, California. We also lease data center facilities in the United States pursuant to various lease agreements and co-location arrangements with data center operators. We believe our facilities are sufficient for our current needs.

Item 3. LEGAL PROCEEDINGS

Legal Proceedings

We are currently a party to a consolidated shareholder class action lawsuit (captioned Doris Shenwick, et al. v. Twitter, Inc., et al. and Claire Degenhardt, et al. v. Twitter, Inc., et al.) that was filed in September 2016 in the U.S. District Court for the Northern District of California. Plaintiffs allege false and misleading statements in violation of securities laws, naming us, a current officer and a former officer as defendants and seek unspecified damages. We filed a motion to dismiss, which was granted in part and denied in part. We dispute the claims and intend to continue to defend the lawsuit vigorously.

We are also currently involved in, and may in the future be involved in, legal proceedings, claims, investigations, and government inquiries arising in the ordinary course of business. These proceedings, in the form ofwhich include both individual and class action litigation and administrative proceedings, have included, but are not limited to matters involving content on the platform, intellectual property, defamation, privacy, securities, employment and contractual rights.

Legal risk is enhanced in certain jurisdictions outside the United States where our protection from liability for content published on our platform by third parties may be unclear and where we may be less protected under local laws than we are in the United States. Future litigation may be necessary, among other things, to defend ourselves, and our users, by determining the scope, enforceability, and validity of third-party rights or to establish our rights.

Although the results of the legal proceedings, claims, investigations, and government inquiries in which we are involved cannot be predicted with certainty, we do not believe that there is a reasonable possibility that the final outcome of these matters will have a material adverse effect on our business, financial condition, operating results, or prospects.  However, the final results of any current or future proceeding cannot be predicted with certainty, and until there is final resolution on any such matter that we may be required to accrue for, we may be exposed to loss in excess of the amount accrued. Regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs, diversion of management resources, and other factors.

Item 4. MINE SAFETY DISCLOSURE

Not applicable.

PART II

Item 5. MARKET FOR REGISTRANT’S COMMON EQUITY RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES

Market Information for Common Stock

Our common stock has been listed on the New York Stock Exchange under the symbol “TWTR” since November 7, 2013. Prior to that date, there was no public trading market for our common stock. The following table sets forth the high and low sales price per share of our common stock as reported on the New York Stock Exchange for the periods indicated:

Holders of Record

As of February 17, 2017,8, 2018, there were 925898 holders of record of our common stock. Because many of our shares of common stock are held by brokers and other institutions on behalf of stockholders, we are unable to estimate the total number of stockholders represented by these record holders.

Dividend Policy

We have never declared or paid any cash dividends on our capital stock. We intend to retain any future earnings and do not expect to pay any dividends in the foreseeable future. Any future determination to declare cash dividends will be made at the discretion of our board of directors, subject to applicable laws, and will depend on a number of factors, including our financial condition, results of operations, capital requirements, contractual restrictions, general business conditions and other factors that our board of directors may deem relevant. In addition, the credit facility contains restrictions on payments including cash payments of dividends.

Unregistered Sales of Equity Securities

From January 1, 2016 through December 31, 2016, we issued an aggregate of 3,676,026 shares of our common stock to a strategic partner and in connection with our acquisitions of certain companies or their assets.

None of the foregoing transactions involved any underwriters, underwriting discounts or commissions, or any public offering. We believe the offers, sales and issuances of the above securities were exempt from registration under the Securities Act by virtue of Section 4(2) of the Securities Act because the issuance of securities to the recipients did not involve a public offering. The recipients of the securities in each of these transactions represented their intentions to acquire the securities for investment only and not with a view to or for sale in connection with any distribution thereof, and appropriate legends were placed upon the stock certificates issued in these transactions. All recipients had adequate access, through their relationships with us, to information about us. The sales of these securities were made without any general solicitation or advertising.None.

Performance Graph

This performance graph shall not be deemed “soliciting material” or to be “filed” with the SEC for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (Exchange Act), or otherwise subject to the liabilities under that Section, and shall not be deemed to be incorporated by reference into any filing of Twitter, Inc. under the Securities Act of 1933, as amended, or the Exchange Act.

The following graph compares the cumulative total return to stockholders on our common stock relative to the cumulative total returns of the Standard & Poor’s 500 Index, or S&P 500, and the Dow Jones Internet Composite Index, or DJ Internet Composite. An investment of $100 (with reinvestment of all dividends) is assumed to have been made in our common stock and in each index on November 7, 2013, the date our common stock began trading on the NYSE, and its relative performance is tracked through December 31, 2016.2017. The returns shown are based on historical results and are not intended to suggest future performance.

Item 6. SELECTED FINANCIAL DATA

The following selected historical consolidated financial data should be read in conjunction with Part II, Item 7, “Management’s Discussion and Analysis of Financial Condition and Results of Operations”, our consolidated financial statements and the related notes included in Item 8, “Financial Statements and Supplementary Data” of this Annual Report on Form 10-K.

The consolidated statements of operations data for the years ended December 31, 2017, 2016 2015 and 20142015 and the consolidated balance sheet data as of December 31, 20162017 and 20152016 are derived from our audited consolidated financial statements included in Part II, Item 8, “Financial Statements and Supplementary Data” in this Annual Report on Form 10‑K. The consolidated statements of operations data for the yearyears ended December 31, 20132014 and 20122013 and the consolidated balance sheet data as of December 31, 2015, 2014 2013 and 20122013 are derived from our audited consolidated financial statements not included in this Annual Report on Form 10-K. Our historical results are not necessarily indicative of the results that may be expected in the future.

Non-GAAP Financial Measures

To supplement our consolidated financial statements presented in accordance with generally accepted accounting principles in the United States, or GAAP, we consider certain financial measures that are not prepared in accordance with GAAP, including Adjusted EBITDA, Adjusted EBITDA margin,non-GAAP income (loss) before income taxes, non-GAAP provision (benefit) for income taxes as it relates to the calculation of non-GAAP net income (loss), revenue on a constant currency basis and advertising revenue on a constant currency basis.non-GAAP net income (loss). These non-GAAP financial measures are not based on any standardized methodology prescribed by GAAP and are not necessarily comparable to similarly-titled measures presented by other companies.

Adjusted EBITDA

We define Adjusted EBITDA as net lossincome (loss) adjusted to exclude stock-based compensation expense, depreciation and amortization expense, interest and other expenses, net, provision (benefit) for income taxes, and restructuring charges and one-time nonrecurring gain, if any. Adjusted EBITDA margin is calculated by dividing Adjusted EBITDA by revenue.

The following table presents a reconciliation of net loss to Adjusted EBITDA for each of the periods indicated:

Non-GAAP Net Income (Loss)

We define non-GAAP net income (loss) as net lossincome (loss) adjusted to exclude stock-based compensation expense, amortization of acquired intangible assets, non-cash interest expense related to our convertible notes, non-cash expense related to acquisitions, impairment of investments in privately-held companies, restructuring charges and one-time nonrecurring gain, and adjustment to income tax effectsexpense based on the non-GAAP measure of profitability using our blended U.S. statutory tax rate (which was 37% for all current and historical periods presented).

Non-GAAP Income (Loss) before Income Taxes.We define non-GAAP income (loss) before income taxes as income (loss) before income taxes adjusted to exclude stock-based compensation expense, amortization of acquired intangible assets, non-cash interest expense related to convertible notes, non-cash expense related to acquisitions, impairment of investments in privately-held companies, and restructuring charges.charges and one-time nonrecurring gain.

Non-GAAP Provision (Benefit) for Income Taxes. We define non-GAAP provision (benefit) for income taxes as the current and deferred income tax expense commensurate with the non-GAAP measure of profitability using our blended U.S. statutory tax rate (which was 37% for all current and historical periods presented).

The following table presents a reconciliation of net loss to non-GAAP net income (loss) for each of the periods indicated: