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 every Interactive Data File required to be submitted 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 such files).    Yes  ☒    No   ☐

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

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.  ☐

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 monetizable daily active usage or users*,users, or mDAU, 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 mDAU, changes in ad engagements and changes in cost per ad engagement.

We define mDAU as people, organizations, or other accounts who logged in or were otherwise authenticated and accessed Twitter on any given day through twitter.com or Twitter applications that are able to show ads. Average mDAU for a period represents the number of mDAU on each day of such period divided by the number of days for such period. Changes in mDAU are a measure of changes in the size of our daily logged in or otherwise authenticated active total accounts. To calculate the year-over-year change in mDAU, we subtract the average mDAU for the three months ended in the previous year from the average mDAU for the same three months ended in the current year and divide the result by the average mDAU for the three months ended in the previous year. We believe that mDAU, and its related growth, are the best ways to measure our success against our objectives and to show the size of our audience and engagement going forward. Additionally, our calculation of mDAU is not based on any standardized industry methodology and is not necessarily calculated in the same manner or comparable to similarly titled measures presented by other companies. Similarly, our measures of mDAU growth and engagement may differ from estimates published by third parties or from similarly-titled metrics of our competitors due to differences in methodology.

The numbers of mDAU 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 engagement across our large number of total accounts 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 the average of false or spam accounts during the fourth quarter of 20192020 represented fewer than 5% of our mDAU during the quarter. The false or spam accounts for a period represents the average of false or spam accounts in the samples during each monthly analysis period during the quarter. 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 mDAU, and 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. We intend to continue to make such improvements. After we determine an account is spam, malicious automation, or fake, we stop counting it in our mDAU, or other related metrics. We also treat multiple accounts held by a single person or organization as multiple mDAU 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 mDAU may not accurately reflect the actual number of people or organizations using our platform.

In addition, geographic location data collected for purposes of reporting the geographic location of our mDAU is based on the IP address or phone number associated with the account when an account is initially registered on Twitter. The IP address or phone number may not always accurately reflect a person’s actual location at the time they engaged with our platform (forplatform. For example, someone accessing Twitter from the location of the proxy server that the person connects to rather than from the person’s actual location).location.

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

Item 1. BUSINESS

Overview

Twitter is what’s happening in the world and what people are talking about right now. From breaking news and entertainment, to sports, politics, and everyday interests, Twitter shows every side of the story. On Twitter you can join the open conversation and watch highlights, clips, or live-streaming events. Twitter is available in more than 40 languages around the world. The service can be accessed via twitter.com, an array of mobile devices via Twitter owned and operated mobile applications (e.g. Twitter for iPhone and Twitter for Android), and SMS.

Our primary product, 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. Through Topics, Trends,Interests, and Moments,Trends, we help people discover what’s happening live. We also continue to implement live broadcasts and on-demand video content across Twitter, including through partnerships with media outlets and our platform partners. Media outlets and our platform partners also help extend the reach of Twitter content by distributing Tweets beyond our products to complement their content. Periscope is a mobile application that lets anyone broadcast and watch video live with others. Periscope broadcastsPeople can also be viewed through Twitterexpress themselves using creation tools like Voice Tweets and on desktopFleets, which allows everyone to start conversations in a new way – with their voice or mobile web browsers.with their fleeting thoughts using text, reactions to Tweets, photos or videos.

In 2019,2020, we improvedcontinued our machine-learning modelswork to provide more relevant content in people’s Home timelinesserve the public conversation by helping people find trusted sources of information and notifications. We are making it easier forbetter organizing and surfacing the many topics and interests that bring people to find what theyTwitter. We are looking for when they come to Twitter by better organizing content around topics and events, and making it easier to follow and join conversations. We also continue to enhanceparticipate in healthier conversations by rolling out new conversation settings globally, and giving people everywhere more control over the public conversation around eventsconversations they start on Twitter with live and on-demand video content, including short videos and highlights, across sports, entertainment, news, and politics.Twitter. In addition, we continuedmade significant progress on our work to innovate fasterbrand and deliver better returns for advertisers by shipping newdirect response roadmap with updated ad platform services as part of our effort to rebuild our core ad server. In 2019, weformats, stronger attribution, and improved targeting. We also continued to iterate on our revamped Mobile Application Promotion (MAP) offering. We furthered our efforts to improve the health of the platform, as we work to make sure that people and advertisers feel safe being a part of the conversation and are able to find credible information on our service. Major areas of focus within health include working to proactively limit the visibility of unhealthy content,reducing abuse, providing more context around misinformation, and protecting the integrity of election-related conversations and giving people more control over theircivic-related conversations. We also launched the Twitter Privacy Center to provide more clarity around what we are doing to protect the information people share with us.

Products and Services for Advertisers

Our Promoted Products enable our advertisers to launch products and services and promote their brands, amplify their visibility and reach, and connect with what’s happening to extend the conversation around their advertising campaigns. We enable our advertisers to target an audience based on a variety of factors, including interest graphs. Interest graphs map, among other things, interests based on who an account follows and actions taken on our platform, such as Tweets created and engagement with Tweets. We believe a person's interest graphthis data produces a clear and real-time signal of that person's interests, greatly enhancing the relevance of the ads we can display 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 people on Twitter as organic content on our platform.

Currently, our Promoted Products consist of:

Advertisers can also run short video ads, such as In-Stream video ads either before or around premium video content, such as during live premium video content from publishing partners or clips from a variety of interest categories such as news, sports and entertainment. Our technology dynamically inserts those advertisers' 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. In addition, In-Stream VideoAmplify Sponsorships allow advertisers to build brand association by sponsoring premium video content from a single publishing partner, including live video, video clips, and other storytelling formats like Sponsored Moments.

We continue to focus our investment on features that differentiate Twitter and capitalize on our value proposition for advertisers, including videoadvertisers. We made progress on our brand and more organicdirect response roadmap, with updated ad formats, stronger attribution, and improved targeting. We expect our acquisition of CrossInstall will accelerate key work streams in direct response. CrossInstall brought a performance ads-focused team to Twitter, added a successful and performant demand-side platform (DSP), and should also help us with our strategy to build and improve MAP and performance ad formats. In addition, we expect CrossInstall will help us increase the value MoPub offers to mobile app developers.

Our technology platform and information database enable us to provide targeting capabilities based on audience attributes like geography, interests, keyword, conversation, content, and events 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 enables customers to advertise across the mobile ecosystem, both on Twitter’sTwitter's owned and operated properties as well as off Twitter on third-party publishers’ websites, applications and other offerings. We enable advertisers to extend their reach beyond Twitter through:

Content Partnerships

Video is an important way to stay informed on Twitter, enabling people on Twitter and content owners to better share experiences, engage in events, and converse with broader audiences. We continue to increase reach and engagement for content owners around the world through live-streaming, highlight video clips, and video-on-demand agreements designed to complement the content from people on Twitter and licensed live and on-demand video content already available on Twitter across a number of verticals including sports, news, gaming and entertainment.

Products for Developers and Data Partners

We provideDeveloper and Enterprise Solutions (DES) is our software-as-a-service platform that enables developers with a platform which they canto build products around the aggregated, anonymized wealth of data on Twitter. Developers use to access a set of tools and publicTwitter application programming interfaces (APIs) to build applications and other products that leverage Twitter data, contribute their content to our platform,for themselves, consumers, and syndicatebusiness customers. DES serves commercial and distribute Twitter content across their properties. In addition, the developer platform is also used by academic researchers who seek to study the public conversation.non-commercial developers including businesses, academics, and consumer developers, among others. We believe this work has the potential to help us with our efforts to improve the health of the public conversation. Websites and applications integrating with our publicly available APIs expands Twitter'simprove people’s experience on Twitter by helping brands and publishers engage with what’s happening and gain insights from the public conversation.

We also offer paid enterprise access to our public data streams for partners with commercial use cases and those who wish to access more data beyond what is available for free. Paying DES customers typically sign multi-year subscriptions or enterprise agreements, based on the type and volume of usage. Our enterprise data products and services offer more sophisticated data analysis tools and other services to support developers in building mature businesses on our platform. Our customer-centric approach positions both Twitter and our key partners for greater growth and monetization, and we are investing in deeper partnerships with select solution providers to help businesses and organizations realize greater value from our data and reach for brands engaging with people who use Twitter, as well as helps to improve the experience people have on Twitter. Many 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.platform. The goal of our platform product development is to make it easy for developers to integrate seamlessly with Twitter, while protecting the privacy and safety of the people who use Twitter.

Competition

Our business is characterized by rapid technological change, frequent product innovation and the continuously evolving preferences and expectations of people on Twitter, advertisers, content partners, platform partners and developers. 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, and to attract and retain marketers, content and platform partners, and developers. 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 for people’s 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 highly competitive. See the sections titled “Risk Factors—If we are unable to compete effectively for people to use our platform, and for content and data partners, our business and operating results could be harmed”harmed.”, “Risk Factors—If we are unable to compete effectively for advertising spend, our business and operating results could be harmed.” and “Risk Factors—We depend on highly skilled personnel to grow and operate our business. If we are unable to hire, retain and motivate our personnel, we may not be able to grow effectively.”  "

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 messages, including images and video, 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. We also continue to invest in protecting the safety, security and integrity of our platform by investing in both people and technology, including machine learning.

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 assist 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.

We use marketing campaigns to help drive audiences to our platform. In 2019,2020, we deliveredcontinued to deliver marketing campaigns focused on celebrating and highlighting the voices of the people who make Twitter unique.

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.

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, data protection, security, rights of publicity, content regulation, data localization, intellectual property, competition, protection of minors, consumer protection, credit card processing, taxation or other subjects. Many of these laws and regulations impacting our business are being proposed, are still evolving andor are being tested in courts and could 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. 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.

WeWith regard to privacy, data protection and security, we are also subject to a variety of federal, state and foreign laws regarding privacy and data protection.regulations. For example, the California Consumer Privacy Act or CCPA,(CCPA), which went into effect on January 1, 2020. The CCPA2020, requires covered companies to, among other things, provide new disclosures to California consumers, and afford such consumers new abilities to opt-out of certain sales of personal information. Similar legislation has been proposed or adopted in other states. Additionally, a new California ballot initiative, the California Privacy Rights Act (CPRA), was passed in November 2020. The CPRA creates obligations relating to consumer data beginning on January 1, 2022, with implementing regulations expected on or before July 1, 2022, and enforcement beginning July 1, 2023. Aspects of the CCPA, the CPRA and these other state laws and regulations, as well as their interpretation and enforcement, remain unclear, and we may be required to modify our practices in an effort to comply with them. Foreign data protection, privacy, security, consumer protection, content regulation and other laws and regulations are often more restrictive or burdensome than those in the United States. For example, the General Data Protection Regulation, or the GDPR, imposes 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.

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 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. On July 28, 2020, we received a draft complaint from the FTC alleging violation of the order and the Federal Trade Commission Act (FTC Act). The allegations relate to our use of phone number and/or email address data provided for safety and security purposes for targeted advertising during periods between 2013 and 2019. The matter remains unresolved, and there can be no assurance as to the timing or the terms of any final outcome. Violation of other 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.

People 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 and certain of our SMS messages have been blocked in Saudi Arabia. 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.indefinitely, including because of our decisions with respect to the enforcement of our rules. 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 mDAU growth, mDAU 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 from the fourth quarter to the subsequent first quarter.

As of December 31, 2019, our backlog primarily consists of long-term data licensing contracts. We generate the substantial majority of our revenue from our advertising services. As such,2020, we do not believe that our backlog, as of any particular date, is necessarily indicative of actual revenue for any future period. Refer to Note 3 of the Notes to Consolidated Financial Statements under Part II, Item 8 of this Annual Report on Form 10-K regarding the amount of remaining performance obligations, which represents the significant majority of our contracted backlog.

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.

Our website is located at https://www.twitter.com, and our investor relations website is located at https://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 SEC website is https://www.sec.gov.

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, @nedsegal, @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

Our mDAU and their level of engagement with advertising are critical to our success and our long-term financial performance will continue to be significantly determined by our success in increasing the growth rate of our mDAU as well as the number of ad engagements. Our mDAU growth rate has fluctuated over time, and it may slow or decline. To the extent our mDAU growth rate slows or the absolute number of mDAU declines, our revenue growth will become dependent on our ability to increase levels of engagement on Twitter, generate advertiser demand, and increase revenue growth from third-party publishers’ websites and applications, data licensing and other offerings. We generate a substantial majority of our revenue based upon engagement with the ads that we display. A number of factors have affected and could potentially negatively affect mDAU growth and engagement, including if:

The substantial majority of our revenue is currently generated from third parties advertising on Twitter. We generate substantially all of our advertising revenue through the sale of our 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. As a result of the COVID-19 pandemic, we experienced a reduction in advertiser demand in the first half of 2020 compared to the same period in 2019. In the second half of 2020, revenue increased compared to the same period in 2019 as advertisers increased their investment on Twitter, engaging our larger audience around the return of events as well as increased and previously delayed product launches. However, we may experience reduced advertiser demand and decreased advertising revenue in future quarters due to the ongoing and potential future impacts of the COVID-19 pandemic.

In addition, many of our advertisers purchase our advertising services through one of several large advertising agencies' 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. Further, our advertisers’ ability to effectively target their advertising to our audience’s interests may be impacted by the degree to which people on Twitter agree in our settings to certain types of personalization or ad targeting, which could have an impact on our revenue. People that already have accounts may change their choices as a result of changes to our privacy control settings that we have implemented or may implement in the future, and people new to Twitter may choose varied levels of personalization, whether in connection with future changes we make to product privacy settings, regulations, regulatory actions, the customer experience, or otherwise.

Changes to operating systems’ practices and policies, such as Apple’s upcoming iOS 14 update that will overhaul their Identifier for Advertisers (IDFA), which helps advertisers assess the effectiveness of their advertising efforts, may also reduce the quantity and quality of the data and metrics that can be collected or used by us and our partners or harm our ability to target advertising. These limitations may adversely affect both our and our advertisers' ability to effectively target advertisements and measure their performance, which could reduce the demand and pricing for our advertising products and harm our business. The impact of these proposed changes on the overall mobile advertising ecosystem, our business, and the developers, partners, and advertisers in the ecosystem is not yet clear. Over time, personalization rates will impact our ability to grow our performance advertising business. Advertisers also may choose to use 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.

Our advertising revenue growth is primarily driven by increases in mDAU, increases in ad pricing or number of ads shown and increases in our clickthrough rate. Although we experienced increased mDAU and ad engagement growth since the start of the COVID-19 pandemic, we experienced a decline in revenue in the first half of 2020 compared to the same period in 2019 due to a reduction in advertiser demand on our platform. In the second half of 2020, revenue increased compared to the same period in 2019 as advertisers increased their investment on Twitter. 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 our mDAU or monetize our larger global audience. Our advertising revenue also could be affected by a number of other factors, including advertiser reaction to content published on our platform or our policies and responses thereto, bugs or other product issues that may impact our ability to effectively help advertisers target ads or share data with our measurement and ad partners. The occurrence of any of these 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 adversely impact our revenue, business, financial condition and operating results.

We face intense competition for people to use our platform, and for content and data partners and advertising spend.partners. We compete for our audience against a variety of social networking platforms, messaging companies and media companies, some of which have greater financial resources, larger audiences or more established relationships with advertisers, such as Facebook (including Instagram and WhatsApp), Alphabet (including Google and YouTube), Microsoft (including LinkedIn), Snap,Snapchat, TikTok, and Verizon Media Group, or in certain regions WeChat, Kakao and Line. New or existing competitors may draw people towards their products or services and away from ours by introducing new product features, including features similar to those we offer, investing their greater resources in audience acquisition efforts or otherwise developing products or services that audiences choose to engage with rather than Twitter, any of which could decrease mDAU growth or engagement and negatively affect our business.

We also compete with respect to content generated by our content partners and the availability of applications developed by platform partners. We may not establish and maintain relationships with content partners who publish on our platform or platform partners who develop applications that integrate with our platform. Our content and platform partners may choose to publish content on, or develop applications for, other platforms, and if they cease to utilize our platform or decrease their use of our platform, then mDAU, engagement, and advertising revenue may decline.

We also face significant competition for advertiser spend. We compete against online and mobile businesses and traditional media outlets, such as television, radio and print, for advertising budgets. We also compete with advertising networks, exchanges, demand side platforms and other platforms, such as Google AdSense, DoubleClick Ad Exchange, Nexage and Brightroll Ad Exchanges, Verizon Media Group, 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.

If we are not able to compete effectively for audience, content and platform partners, and advertiser spend, our mDAU and engagement would decline and our business and operating results would be materially and adversely impacted.

We believe that our long-term success depends on our ability to improve the health of the public conversation on Twitter. We have made this one of our top priorities and have focused our efforts on improving the quality of that conversation, including by devoting substantial internal resources to our strategy. These efforts include the reduction of abuse, harassment, spam, manipulation and malicious automation on the platform, as well as a focus on improving information quality (including information around the 2020 U.S. elections), and the health of conversation on Twitter. Some of the health initiatives that we have implemented as part of our ongoing commitment to a healthy public conversation have negatively impacted, and may in the future negatively impact, our publicly reported metrics in a few ways.

First, our health efforts include the removal of accounts pursuant to our terms and services that are abusive, spammy, fake or malicious, and these accounts may have been included in our mDAU, as well as actions taken to detect and challenge potentially automated, spammy or malicious accounts during the sign-up process. For example,If we make a sudden improvement to one of the algorithms we use to detect spammy or suspicious behavior, we may remove a larger number of accounts as a result and impact the year-over-year average of mDAU growth. Additionally, we may remove certain influential accounts for violations of our terms of service and the removal of such accounts has in the thirdpast reduced and fourth quarters of 2018, year-over-year averagemay in the future reduce our mDAU growth was impacted by ongoing health efforts, both due to how we resourced and prioritized our work and the impact from ongoing success removing spammy and suspicious accounts.

Second, we are also making active decisions to prioritize certain health related initiatives over other near-term product improvements that may drive more usage of Twitter as a daily utility. These decisions may not be consistent with the short-term expectations of our advertising customers or investors and may not produce the long-term benefits that we expect, in which case our mDAU growth and engagement, our relationships with advertisers and our business and operating results could be harmed.

From time to time, we have also experienced high voluntary attrition, and in those times, the resulting influx of new leaders and other employees has required us to expend time, attention and resources to recruit and retain talent, restructure parts of our organization and train and integrate new employees. In addition, to attract and retain skilled personnel, we have had to offer, and believe we will need to continue to offer, highly competitive compensation packages. We may need to invest significant amounts of cash and equity to attract and retain new employees and we may not realize sufficient 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 and 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. We recently announced that employees will be able to work from home permanently if they so desire and we expect that we will continue to hire employees that are not located where we have offices or will work from home. 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 would be adversely impacted.

One of the reasons people come to Twitter every day is for real-time information, and our products and the success of our business is dependent upon the ability of people to access the Internet and the proper functioning of the various operating systems, platforms, and services upon which we rely. These systems are provided and controlled by factors outside of our control, including nation-state actors who may suppress or censor our products, and 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 these actors could take actions that degrade, disrupt or increase the cost of 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 past, 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. We utilize third-party cloud computing services in connection with certain aspects of our business and operations, and any disruption of, or interference with, our use of such cloud services could adversely impact our business and operations. As the Internet continues to experience growth in the number of consumers, frequency of use and amount of data transmitted, the Internet infrastructure that we rely on may be unable to support the demands placed upon it. The failure of the Internet infrastructure that we rely on, even for a short period of time, could undermine our operations and harm our operating results.

Furthermore, these systems, devices or software or services may experience changes, bugs or technical issues that may affect the availability of services or the accessibility of our products. 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. In the past, we have experienced brief service outages during which Twitter.com and Twitter mobile clients were inaccessible as a result, in part, of software misconfigurations. 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.

“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 people with the general goal of drawing attention to a given account, site, product or idea. This includes posting large numbers of unsolicited mentions of an account, 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-followingunfollowing accounts, adding accounts 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 accounts seeking to promote themselves on Twitter. Although we continue to invest resources to reduce spam and fake accounts on Twitter, which includes our investments to improve the health of the public conversation 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 accounts on our platform will result in increased efforts by spammers to misuse our platform. We continuously combat spam and fake accounts, 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 and fake accounts require significant resources and time. If spam and fake accounts increase on Twitter, this could hurt our reputation for delivering relevant content or reduce mDAU growth rate and mDAU engagement and result in continuing operational cost to us.

Our products and services involve the storage and transmission of people's and advertisers’ information, and security incidents, including those caused by unintentional errors and those intentionally caused by third parties, may expose us to a risk of loss of this information, litigation, increased security costs and potential liability. We and our third-party service providers experience cyber-attacks of varying degrees on a regular basis. We expect to incur significant costs in an effort to detect and prevent security breaches and other security-related incidents, including those that our third-party suppliers and service providers may suffer, and we may face increased costs in the event of an actual or perceived security breach or other security-related incident. In particular, the COVID-19 pandemic is increasing the opportunities available to criminals, as more companies and individuals work online, and as such, the risk of a cybersecurity incident potentially occurring is increasing. We cannot provide assurances that our preventative efforts will be successful. If an actual or perceived breach of our security occurs, the market perception of the effectiveness of our security measures could be harmed, people on Twitter and our 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. While our insurance policies include liability coverage for certain of these matters, if we experienced a significant security incident, we could be subject to liability or other damages that exceed our insurance coverage.

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 2019, we discovered, and took steps to remediate, bugs that primarily affected our legacy MAP product, impacting our ability to target ads and share data with our measurement and ad partners. We also discovered that certain personalization and data settings were not operating as expected. As was the case with these errors, 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 people on Twitter, partners 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 the people on Twitter and/or our intellectual property or lead to reductions in our ability to provide some or all of our services. Any errors, bugs or vulnerabilities discovered in our code after release could result in damage to our reputation, loss of accounts, 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 impact our business and operating results.

Unauthorized parties may also gain access to Twitter handles and passwords without attacking Twitter directly and, instead, access people’s accounts by using 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-party applications to which people have given permission to Tweet on their behalf, may receive or store information provided by us or by people on Twitter 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 data of people on Twitter may be improperly accessed, used or disclosed. Unauthorized parties have obtained, and may in the future obtain, access to our data, data of people on Twitter or our advertisers’ data. Any systems failure or actual or perceived compromise of our security that results in the unauthorized access to or release of data of people on Twitter or our 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.

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, mDAU may grow more rapidly than revenue in international regions where our monetization of our products and services is not as developed. For example, average mDAU outside the United States constituted 80% of our average mDAU in the three months ended December 31, 2019, but our international revenue, as determined based on the billing location of our customers, was approximately 41% of our consolidated revenue in the three months ended December 31, 2019. Our inabilityIf we are unable to successfully expand our business, manage the complexity of our global operations or monetize our products and services internationally, it could adversely impact our business, financial condition 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 resultIn 2020, as well as other periods in claims, changes to our business practices, monetary penalties, increased cost of operations or declines in mDAU growth, mDAU engagement or ad engagement, or otherwise harm our business.

Given the rapidly evolving markets in which we compete, our historical operating results may not be useful to complyyou in predicting our future operating results. If our revenue growth rate slows, we expect that the seasonality in our business may result,become more pronounced and may 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 affectthe future cause our business.operating results to fluctuate. For example, advertising spending is traditionally seasonally strong in the California Consumer Privacy Act ("CCPA") went into effect on January 1, 2020. The CCPA requires, amongfourth 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. Additionally, certain new revenue products or product features may carry higher costs relative to our other things, covered companies to provide new disclosures to California consumers and afford such consumers new abilities to opt-out of certain sales of personal information. Similar legislation has been proposed or adopted in other states. Aspects of the CCPA and these other state laws and regulations, as well as their enforcement, remain unclear,products, which may decrease our margins, and we may be requiredincur increased costs to modifyscale our practices in an effort to comply with them. Moreover, foreign data protection, privacy, consumer protection, content regulationoperations if mDAU and other laws and regulations are often more restrictive or burdensome than those in the United States. For example, the GDPR imposes 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, whichever is higher. Additionally, we relyengagement on a variety of legal bases to transfer certain personal information outside of the European Economic Area, including the EU-U.S. Privacy Shield Framework, the Swiss-U.S. Privacy Shield Framework, and EU Standard Contractual Clauses, or SCCs. These legal bases all have been, and may be, the subject of legal challenges and they may be modified or invalidated. This could result in us being required to implement duplicative, and potentially expensive, information technology infrastructure and business operations in Europe or could limit our ability to collect or process personal information in Europe. Any of these changes with respect to EU data protection law could disrupt our business.

We calculate our mDAU 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 mDAU and mDAU engagement. For example, there are a number of false or spam accounts in existence on our platform. We estimate that the average of false or spam accounts during the fourth quarter of 2020 continued to represent fewer than 5% of our mDAU during the quarter. 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 mDAU, but we otherwise treat multiple accounts held by a single person or organization as multiple accounts for purposes of calculating our mDAU 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 mDAU may not accurately reflect the actual number of people or organizations using our platform. We regularly review and may adjust our processes for calculating our internal metrics to improve their accuracy. Our measures of mDAU growth and 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 without the collectionpartners or investors do not perceive our metrics to be accurate representations of extensive personal information. Weour total accounts or mDAU engagement, or if we discover material inaccuracies in our metrics, our reputation may experience additional pressurebe harmed and content partners, advertisers and platform partners may be less willing to expandallocate their budgets or resources to our collection of personal information in order to comply with newproducts and additional legal or regulatory demands orservices, which could negatively affect our business and operating results. Further, as our business develops, we may independently decide torevise or cease reporting metrics if we determine that such metrics are no longer accurate or appropriate measures of our performance. If investors, analysts or customers do so. If we obtainnot believe our reported measures, such additional personal information,as mDAU, are sufficient or accurately reflect our business, we may receive negative publicity and our operating results may be subject to additional legal or regulatory obligations.

A significant natural disaster, such as the COVID-19 pandemic or an earthquake, fire, flood or significant power outage could cause us to incur additional expenses or changehave a material adverse impact on our business, practicesoperating results, and financial condition. For example, the COVID-19 pandemic has led to certain business disruptions as described in our other risk factors, including travel bans and restrictions, shelter-in-place orders and the postponement or cancellation or major events, which have adversely affected demand for our advertising products and the economy as a manner materialwhole, and which may continue to have an adverse toeffect on our business.

As accounts generate more content, including photos and videos hosted by Twitter, we have been subjectmay be required to regulatory investigations,expand and we expectadapt our technology and infrastructure to continue to be subjectreliably store, serve and analyze this content. It may become increasingly difficult to regulatory scrutinymaintain and improve the performance of our products and services, especially during peak usage times, as our business growsproducts and awareness ofservices become more complex and our brandaccount traffic increases.

We may face lawsuits or incur liability as a resultcontinue to scale the capacity of, content published or made available throughand enhance the capability and reliability of, our productsinfrastructure to support mDAU growth and services.

Intellectual property rights are important assets of our business and we seek protection for such rights as appropriate. To establish and protect our trade secrets, trademarks, copyrights, and patents as well as restrictions in confidentiality, license and intellectual property assignment agreements we enter into with our employees, consultants and third parties. Various circumstances and events outside of our control, however, pose threats to our intellectual property rights. We may fail to obtain effective intellectual property protection, effective intellectual property protection may not be available in every country in which our products and services are available, or such laws may provide only limited protection. 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, circumvented, infringed or misappropriated 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 restrictions on the use and disclosure of our trade secrets and other proprietary information contained in agreements we sign with our employees, contractors, and other third parties to limit and control access to and disclosure of our trade secrets and confidential information. These agreements may be breached, or this intellectual property may otherwise be disclosed or become known to our competitors, including through hacking or theft, which could cause us to lose any competitive advantage resulting from these trade secrets and proprietary information.

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. 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. We have a policy designed to assist third parties in the proper use of our trademarks, and an internal team dedicated to enforcing this policy and protecting our brand. This team routinely reviews reports of improper and unauthorized use of the Twitter trademarks 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 or trademarks. If the licensees of our trademarks are not using our trademarks properly and we fail to maintain and enforce our trademark rights, we may limit our ability to protect our trademarks which could result in diminishing the value of our brand or in our trademarks being declared invalid or unenforceable. There is also a risk that one or more of our trademarks could become generic, which could result in such trademark 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.

Our Innovator’s Patent Agreement, or IPA, also can 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 to be 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 people on Twitter, or any of our 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 people on Twitter, or any of our 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. In this case, 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 goes to work for another company and that company uses the inventor’s patented invention 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 since it would be unlikely the employee would consent to offensive use of the patent against his or her current employer. In such event, we 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.

Also, obtaining, maintaining and enforcing our intellectual property rights is costly and time consuming. Any increase in the unauthorized use of our intellectual property would adversely impact our business, financial condition and 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 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 develop new products, we expect the number of patent and other intellectual property claims against us may 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 would adversely impact our business, financial condition and operating results.

From time to time, governments, regulators and others have expressed concerns about whether our products, services or practices compromise the privacy or data protection rights of the people on Twitter and others. While we strive to comply with applicable laws and regulations relating to privacy, data protection and data security, our privacy policies and other obligations we may have with respect to privacy, data protection and data security, the failure or perceived failure to 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.

We have faced and will continue to calculate certainface claims relating to content that is published or made available through our products and services or third-party products or services. In particular, the nature of our key metrics,business exposes us to claims related to defamation, intellectual property rights, rights of publicity and realprivacy, illegal content, misinformation, content regulation and personal injury torts. The laws relating to the liability of providers of online products or perceived inaccuracies in such metrics may harm our reputationservices for activities of the people who use them remains somewhat unsettled, both within the United States and negatively affect our business.

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.

In 2014, we issued $954.0 million in aggregate principal amount of 1.00% convertible senior notes due 2021, or the 2021 Notes, in private placements to qualified institutional buyers.Notes. In 2018, we issued an additional $1.15 billion in aggregate principal amount of 0.25% convertible senior notes due 2024, which we refer to asor the Convertible Notes when taken together with the 2021 Notes, in a private placement to qualified institutional buyers.2024 Notes. In December 2019, we issued $700.0 million in aggregate principal amount of 3.875% senior notes due 2027, which we refer to as the 2027 Notes. In March 2020, we issued $1.0 billion in aggregate principal amount of 0.375% convertible senior notes due 2025, or the 2025 Notes. We refer to the 2021 Notes, or, when taken together withthe 2024 Notes and the 2025 Notes as the Convertible Notes, and we refer to the Convertible Notes and the 2027 Notes as the Notes. As of December 31, 2019,2020, we had $2.80$3.80 billion in aggregate principal amount of outstanding Notes. As of December 31, 2019,2020, we also had an undrawn unsecured revolving credit facility providing for loans in the aggregate principal amount of $500.0 million.

Our ability to meet our payment obligations under our debt instruments depends on our ability to generate significant cash flows in the future. This, to some extent, is subject to market, economic, financial, competitive, legislative, and regulatory factors as well as other factors that are beyond our control. There can be no assurance that our business will generate cash flow from operations, or that additional capital will be available to us, in amounts sufficient to enable us to meet our debt payment obligations and to fund other liquidity needs. Additionally, events and circumstances may occur which would cause us to not be able to satisfy applicable draw-down conditions and utilize our revolving credit facility. If we are unable to generate sufficient cash flows to service our debt payment obligations, we may need to refinance or restructure our debt, sell assets, reduce or delay capital investments, or seek to raise additional capital. If we are unable to implement one or more of these alternatives on commercially reasonable terms or at all, we may be unable to meet our debt payment obligations, which would materially and adversely impact our business, financial condition and operating results.

Our income tax obligations are based in part on our corporate operating structure, including the manner in which we develop, value, manage, protect and use our intellectual property and the scope of our international operations. We are subject to review and audit by tax authorities in the United States (federal and state), Ireland, and other foreign jurisdictions and the laws in those jurisdictions are subject to interpretation. Tax authorities may disagree with and challenge some of the positions we have taken and any adverse outcome of such an 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. For example, the legislation commonly referred to as the 2017 Tax Cuts and Jobs Act (the “Tax Act”)Tax Act) significantly affected U.S. tax law by changing how U.S. income tax is assessed on multinational corporations. The U.S. Department of Treasury has issued and will continue to issue regulations and interpretive guidance that may significantly impact how we will apply the law and impact our results of operations.

On June 7, 2019, the Ninth Circuit Court of Appeals issued a newan opinion in the case of Altera Corp. v. Commissioner (Altera), which upheld Department of Treasury regulations which requirerequiring related parties in an intercompany cost-sharing arrangement to share expenses related to stock-based compensation. During the year ended December 31, 2019, we evaluated the Court’s ruling and recorded an increase in the tax provision of $80.0 million. In February 2020, Altera Corp. filed a petition to appeal the decision with the Supreme Court of the United States. We will continueOn June 22, 2020, the Supreme Court denied the petition. In the fourth quarter of 2020, we filed our 2019 U.S. Federal and state tax returns and included certain adjustments related to monitor future developmentsAltera for which we previously recognized a reserve. As a result, our unrecognized tax benefits decreased by $96.9 million in this casethe fourth quarter of 2020 with no impact on our effective tax rate.

As of December 31, 2020, we had U.S. federal net operating loss carryforwards of $2.19 billion and state net operating loss carryforwards of $1.28 billion. As of December 31, 2020, we had federal and state research and development credit carryforwards of $398.4 million and $297.1 million, respectively. A portion of the net operating loss carryforwards and tax credit carryforwards could be subject to ownership change limitations governed by Section 382 or 383 of the consolidatedInternal Revenue Code. Any such limitations on the ability to use our net operating loss carryforwards and other tax assets could adversely impact our business, financial statements.

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 may continue to be highly volatile in response to various factors, some of which are beyond our control. 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 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 Convertible2021 Notes and 2024 Notes, as applicable (and are likely to do so during any applicable observation period related to a conversion of Convertiblethe 2021 Notes and 2024 Notes, as applicable, or following any repurchase of Convertiblethe 2021 Notes and 2024 Notes, as applicable, 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.

Item 1B. UNRESOLVED STAFF COMMENTS

None.

Item 2. PROPERTIES

Facilities

Item 3. LEGAL PROCEEDINGS

Legal Proceedings

We are currently involved in, and may in the future be involved in, legal proceedings, claims, investigations, and government inquiries and investigations arising in the ordinary course of business. These proceedings, which 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, privacy, data protection, consumer protection, securities, employment and contractual rights. Legal risk may be enhanced in 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 the people on Twitter or to establish our rights. For information regarding legal proceedings in which we are involved, see “Legal Proceedings” in Note 16 of the accompanying notesNotes to our consolidated financial statements,Consolidated Financial Statements included in Part II, Item 8 of this Annual Report on Form 10-K, which is incorporated herein by reference.

Item 4. MINE SAFETY DISCLOSURE

Not applicable.

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..

Holders of Record

As of February 6, 2020,9, 2021, there were 825831 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

During the three months ended December 31, 2019,2020, we issued a total of 164,742262,584 shares of our common stock in connection with the acquisition of one company to certain former shareholders of the acquired company.

The foregoing transaction did not involve any underwriters, any underwriting discounts or commissions, or any public offering. We believe the offer, sale, and issuance of the above securities was exempt from registration under the Securities Act of 1933, as amended (the “Act”)Act) by virtue of Section 4(a)(2) of the Act and Regulation S promulgated under the Act, because the issuance of securities to the recipients did not involve a public offering. The recipients of the securities in this transaction 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 this transaction. All recipients had adequate access, through their relationships with us or otherwise, to information about us. The issuance of these securities was made without any general solicitation or advertising.

Performance Graph

The following graph compares the cumulative 5-year 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 at the market close on the last trading day for the fiscal year ended December 31, 20142015 and its relative performance is tracked through December 31, 2019.2020. The returns shown are based on historical results and are not intended to suggest future performance.

FY 2019 Overview and2020 Highlights

Total revenue was $3.46$3.72 billion, an increase of 14%7%, or 15% on a constant currency basis, compared to 2018.2019.

Net loss was $1.14 billion in 2020, which was inclusive of a $1.10 billion provision for income taxes related to the establishment of a valuation allowance against deferred tax assets. Net income was $1.47 billion compared toin 2019, which was inclusive of a $1.21 billion in 2018.

Cash, cash equivalents and short-term investments in marketable securities totaled $6.64$7.47 billion as of December 31, 2019.2020.

Average monetizable daily active usersusage (mDAU) were 152was 192 million for the three months ended December 31, 2019,2020, an increase of 21% year-over-year.27% year over year.

Key Metrics

We review a number of metrics, including the key metrics discussed below, to evaluate our business, measure our performance, identify trends affecting our business, formulate business plans and make strategic decisions.

In the three months ended December 31, 2019,2020, ad engagements increased 29%35% from the three months ended December 31, 2018. The increase was primarily2019, driven by increasedstrong growth in ad impressions driven by audience growth and improved clickthrough rates (CTR), which grew on a year-over-year basis across the majority of ad types due to ongoing improvements in ad relevance.our growing audience and increased demand for ads. In the three months ended December 31, 2019,2020, cost per ad engagement decreased by 13%3% compared to the three months ended December 31, 2018, reflecting a continued mix shift to video ad formats (which have a lower cost per ad engagement) and like-for-like price decreases across most ad formats.

Results of Operations

The following tables set forth our consolidated statement of operations data for each of the periods presented (in thousands):

The following table sets forth our consolidated statement of operations data for each of the periods presented as a percentage of revenue:

Years Ended December 31, 2020, 2019 2018 and 20172018

We generate the substantial majority of our revenue from the sale of advertising services. We also generate revenue by licensing our data to third parties and providing mobile advertising exchange services.

We generate most of our advertising revenue by selling our Promoted Products. Currently, our Promoted Products consist of the following:

While the majority of the Promoted Products we sell to our advertisers are placed on Twitter, we also generate advertising revenue by placing advertising products that we sell to advertisers on third-party publishers’ websites, applications or other offerings.

We generate data licensing and other revenue by (i) offering data products and data licenses that allow our data partners to access, search and analyze historical and real-time data on our platform (which consists of public Tweets and their content), and (ii) providing mobile advertising exchange services through our MoPub exchange. Our data partners generally purchase licenses to access all or a portion of our data for a fixed period. We recognize data licensing revenue as our data partners consume and benefit from their use of the licensed data. In addition, we operate a mobile ad exchange and receive service fees from transactions completed on the exchange. Our mobile ad exchange enables buyers and sellers to purchase and sell advertising inventory and matches buyers and sellers. We have determined we are not the principal as it relates to the purchase and sale of advertising inventory in transactions between third-party buyers and sellers on the exchange. Therefore, we report revenue related to our ad exchange services on a net basis.

In 2019,2020, advertising revenue increased by $376.0$214.0 million or 14%7% compared to 2018. On a constant currency basis, advertising revenue in 2019 would have increased by $401.3 million or 15% compared to 2018.