We have incurred net losses in each year since our inception, including net losses of $26.6 million and $24.5 million in each of the three months ended December 31, 2017 and 2016, and 2015respectively, and net losses of $103.8$110.6 million and $84.1$103.8 million for the fiscal years ended December 31, 20162017 and 2015,2016, respectively. We had an accumulated deficit of $319.7$430.6 million atas of December 31, 2016.2017. For the three months ended December 31, 20162017 and 2015,2016, our revenue was $88.6$123.4 million and $62.6$88.6 million, respectively, representing a 41.5%39% growth rate. For the fiscal years ended December 31, 20162017 and 2015,2016, our revenue was $312.0$430.5 million and $208.8$312.0 million, respectively, representing a 49.4%38% growth rate. We expect that our revenue growth rate will decline over time. We may not be able to generate sufficient revenue to achieve and sustain profitability as we also expect our costs to increase in future periods. We expect to continue to expend substantial financial and other resources on:

We were incorporated and launched our first product in 2007. As a result of our limited operating history, our ability to accurately forecast our future operating results is limited and subject to a number of uncertainties, including our ability to plan for and model future growth. Our historical revenue growth has been inconsistent, and should not be considered indicative of our future performance. Further, in future periods, our revenue could decline for a number of reasons, including any reduction in demand for our products, increased competition, contraction of our overall market, or our failure, for any reason, to capitalize on growth opportunities. We have encountered and will continue to encounter risks and uncertainties frequently experienced by growing companies in rapidly changing industries, such as the risks and uncertainties described herein. If our assumptions regarding these risks and uncertainties, which we use to plan our business, are incorrect or change due to changes in our markets, or if we do not address these risks and uncertainties successfully, our operating and financial results could differ materially from our expectations, and our business could suffer.

The market for customer service solutions is fragmented, rapidly evolving, and highly competitive, with relatively low barriers to entry. With respect to larger organizations and enterprises seeking to deploy a customer service software system, we have many competitors that are larger than us and which have greater name recognition, much longer operating histories, more established customer relationships, larger marketing budgets, and significantly greater resources than we do. Among the small to medium sized organizations that make up a large proportion of our customers, we often compete with general use computer applications and other tools, which these organizations use to provide support and which can be deployed for little or no cost. These include shared accounts for email communication, phone banks for voice communication, and pen and paper, text editors, and spreadsheets for tracking and management. With respect to larger organizations and enterprises seeking to deploy a customer service software system, we have many competitors that are larger than us and which have greater name recognition, much longer operating histories, more established customer relationships, larger marketing budgets, and significantly greater resources than we do.

The market for SaaS business software applications is less mature than the market for on-premise business software applications, and the adoption rate of SaaS business software applications may be slower among subscribers in industries with heightened data security interests or business practices requiring highly customizable application software. Our success will depend to a substantial extent on the widespread adoption of SaaS business applications in general, and of SaaS customer service applications in particular. Many organizations have invested substantial personnel and financial resources to integrate traditional on-premise business software applications into their businesses, and therefore may be reluctant or unwilling to migrate to SaaS applications. It is difficult to predict customer adoption rates and demand for our products, the future growth rate and size of the SaaS business applications market, or the entry of competitive applications. The expansion of the SaaS business applications market depends on a number of factors, including the cost, performance, and perceived value associated with SaaS, as well as the ability of SaaS providers to address data security and privacy concerns. Additionally, government agencies have adopted, or may adopt, laws and regulations regarding the collection, use, and transfer of personal information obtained from consumers and other individuals, or may seek to access information on our platform, either of which may reduce the overall demand for our products. If we or other SaaS providers experience data security incidents, loss of customer data, disruptions in delivery, or other problems, the market for SaaS business applications, including our products, may be negatively affected. If SaaS business applications do not continue to achieve market acceptance, if there is a reduction in demand for SaaS business applications caused by a lack of customer acceptance, or if there are technological challenges, weakening economic conditions, data security or privacy concerns, governmental regulation, competing technologies and products, or decreases in information technology spending, it would result in decreased revenue and our business would be adversely affected.

Use of our products involves the storage, transmission, and processing of our customers’ proprietary data, including personal or identifying information regarding their customers or employees. Unauthorized access to or security breaches of our products could result in the loss of data, loss of intellectual property or trade secrets, loss of business, severe reputational damage adversely affecting customer or investor confidence, regulatory investigations and orders, litigation, or indemnity obligations. Furthermore, if our network or computer systems are breached or unauthorized access to customer data is otherwise obtained, we may be held responsible for damages for contract breach, penalties for violation of applicable laws, regulations, or contractual obligations, and significant costs for remediation that may include liability for stolen assets or information and repair of system damage that may have been caused, incentives offered to customers or other business partners in an effort to maintain business relationships after a breach, and other liabilities. Notifications related to a security breach regarding or pertaining to any of such service providers could impact our reputation, harm customer confidence, hurt our sales and expansion into new markets, or cause us to lose existing customers. We have incurred, and expect to continue to incur, significant expenses to prevent, investigate, and remediate security breaches and vulnerabilities, including deploying additional personnel and protection technologies, training employees, and engaging third-party experts and consultants. Our errors and omissions insurance coverage covering certain security and privacy damages and claim expenses may not be sufficient to compensate for all liability.

Our continued growth depends in part on the ability of our existing and potential customers to access our products at any time and within an acceptable amount of time. Our products are proprietary, and we rely on the expertise of members of our engineering, operations, and software development teams for their continued performance. We have experienced, and may in the future experience, disruptions, outages, and other performance problems due to a variety of factors, including infrastructure changes, introductions of new functionality, human or software errors, capacity constraints due to an overwhelming number of users simultaneously accessing our products, distributed denial of service attacks, or other security related incidents. In some instances, we may not be able to identify the cause or causes of these performance problems within an acceptable period of time. It may become increasingly difficult to maintain and improve our performance, especially during peak usage times and as our products become more complex and our user traffic increases. If any of our products isare unavailable or if our users are unable to access our products within a reasonable amount of time or at all, our business would be negatively affected. In addition, a significant portion of our infrastructure does not currently support the mirroring of data. Therefore, in the event of any of the factors described above, or certain other failures of our infrastructure, customer data may be permanently lost. Moreover, some of our customer agreements and certain subscription plans include performance guarantees and service level standards that obligate us to provide credits or termination rights in the event of a significant disruption in our services. To the extent that we do not effectively address capacity constraints, upgrade our systems as needed, and continually develop our technology and network architecture to accommodate actual and anticipated changes in technology, our business and operating results may be adversely affected.

Because our products are complex, undetected errors, failures, vulnerabilities, or bugs may occur, especially when updates are deployed. Our products are often used in connection with large-scale computing environments with different operating systems, system management software, equipment, and networking configurations, which may cause errors or failures of our products or other aspects of the computing environment into which they are deployed. In addition, deployment of our products into complicated, large-scale computing environments may expose undetected errors, failures, vulnerabilities, or bugs in our products. We have discovered, and expect to continue to discover, software errors, failures, vulnerabilities, and bugs in our products, some of which have or may only be discovered and remediated after deployment to customers. Real or perceived errors, failures, vulnerabilities, or bugs in our products could result in negative publicity, loss of or delay in market acceptance of our products, loss of competitive position, or claims by customers for losses sustained by them. In such an event, we may be required, or may choose, for customer relations or other reasons, to expend additional resources in order to help correct the problem.

Our products are deployed in a wide variety of technology environments and into a broad range of complex workflows. Increasingly, our products have been, and will continue to be, integrated into large-scale, complex technology environments and specialized use cases, and we believe our future success will depend on our ability to increase use of our products in such deployments. We often assist our customers in implementing our products, but many customers attempt to implement deployments, including complex deployments, themselves. If we or our customers are unable to implement our products successfully, or are unable to do so in a timely manner, customer perceptions of our products and of our company may be impaired, our reputation and brand may suffer, and customers may choose not to renew or expand the use of our products.

In deploying and using our products, our customers depend on our product support team and customer success organization to resolve complex technical and operational issues. We may be unable to respond quickly enough to accommodate short-term increases in customer demand for product support. We also may be unable to modify the nature, scope, and delivery of our product support to compete with changes in product support services provided by our competitors. Increased customer demand for product support, without corresponding revenue, could increase costs and adversely affect our operating results. Additionally, we may be unable to develop our customer success organization to continue to support the increasing level of complexity that larger enterprise customers require while maintaining the same level of engagement across all customers.

Our sales are highly dependent on our business reputation and on positive recommendations from our existing customers. Any failure to maintain high-quality product support, or a market perception that we do not maintain high-quality product support, or maintain a high-complexity customer success organization, could adversely affect our reputation, our ability to sell our products to existing and prospective customers, and our business, operating results, and financial position.

Our success depends largely upon the continued services of our executive officers and other key employees. We rely on our leadership team and on individual contributors in the areas of research and development, operations, security, sales, marketing, sales, support, and general and administrative functions. From time to time, there may be changes in our executive management team resulting from the hiring or departure of executives, which could disrupt our business. In 2016, we added three new members to our senior management team, including a new Chief Financial Officer.

We are highly dependent upon our marketing strategy of offering free trials of our products and other inbound lead generation strategies to generate sales opportunities. These strategies may not be successful in continuing to generate sufficient sales opportunities necessary to increase our revenue. Many early users never convert from the trial version of a product to a paid version of such product. Further, we often depend on individuals within an organization who initiate the trial versions of our products being able to convince decision makers within their organization to convert to a paid version. Many of these organizations have complex and multi-layered purchasing requirements. To the extent that these users do not become, or are unable to convince others to become, paying customers, we will not realize the intended benefits of this marketing strategy and our ability to grow our revenue will be adversely affected.

As we target more of our sales efforts to larger organizations, we expect to incur higher costs and longer sales cycles and we may be less effective at predicting when we will complete these sales. In this market segment, the decision to subscribe to one or more of our products may require the approval of a greater number of technical personnel and management levels within a potential customer’s organization than we have historically encountered, and if so, these types of sales would require us to invest more time educating these potential customers on the benefits of our products. In addition, larger organizations may demand more features and integration services. We have limited experience in developing and managing sales channels and distribution arrangements for larger organizations. As a result of these factors, these sales opportunities may require us to devote greater research and development, sales, product support, and professional services resources to individual customers, resulting in increased costs and reduced profitability, and would likely lengthen our typical sales cycle, which could strain our resources. Moreover, these transactions may require us to delay recognizing the associated revenue we derive from these customers until any technical or implementation requirements have been met, and larger customers may demand discounts to the subscription prices they pay for our products. Furthermore, because we have limited experience selling to larger organizations, our investment in marketing our products to these potential customers may not be successful, which could harm our results of operations and our overall ability to grow our customer base. Following sales to larger organizations, we may have fewer opportunities to expand usage of our products or to sell additional functionality, and we may experience increased subscription terminations as compared to our experience with smaller organizations, any of which could harm our results of operations.

We plan our expenses based on certain assumptions about the length and variability of our sales cycle. These assumptions are based upon historical trends for sales cycles and conversion rates associated with our existing customers, many of whom to date have been small to medium-sized organizations that make purchasing decisions with limited interaction with our sales or other personnel. As we continue to become more dependent on sales to larger organizations, we expect our sales cycles to lengthen and become less predictable. This may adversely affect our financial results. Factors that may influence the length and variability of our sales cycle include:

Our quarterly financial results may fluctuate as a result of a variety of other factors, many of which are outside of our control. If our quarterly financial results fall below the expectations of investors or any securities analysts who follow our stock, the price of our common stock could decline substantially. Some of the important factors that may cause our revenue, operating results, and cash flows to fluctuate from quarter to quarter include:

Our operating results may vary based on the impact of changes in our industry or the global economy on us or our customers. The revenue growth and potential profitability of our business depend on demand for business software applications and services generally and for customer service systems in particular. In addition, our revenue is dependent on the number of users of our products, at each of our customers, which in turn is influenced by the employment and hiring patterns of our customers. To the extent that weak economic conditions cause our customers and prospective customers to freeze or reduce their hiring for personnel providing service and support, demand for our products may be negatively affected. Historically, during economic downturns there have been reductions in spending on information technology and customer service systems as well as pressure for extended billing terms and other financial concessions. If economic conditions deteriorate, our customers and prospective customers may elect to decrease their information technology and customer service budgets, which would limit our ability to grow our business and negatively affect our operating results.

To date, we have been primarily dependent on our direct sales force to sell subscriptions to our products. Although we have developed certain channel partners, such as referral partners, resellers, and integration partners, these channels have resulted in limited revenue to date. We believe that identifying, developing, and maintaining strategic relationships with additional channel partners are important to driving revenue growth for our company.company and will continue to dedicate resources to those efforts. Our agreements with our existing channel partners are non-exclusive, meaning our channel partners may offer customers the products of several different companies, including products that compete with ours. They may also cease marketing our products with limited or no notice and with little or no penalty. We expect that any additional channel partners we identify and develop will be similarly non-exclusive and not bound by any requirement to continue to market our products. If we fail to identify additional channel partners, in a timely and cost-effective manner, or at all, or are unable to assist our current and future channel partners in independently selling and deploying our products, our business, results of operations, and financial condition could be adversely affected. Additionally, customer retention and expansion attributable to customers acquired through our channel partners may differ significantly from customers acquired through our direct sales efforts. If our channel partners do not effectively market and sell our products, or fail to meet the needs of our customers, our reputation and ability to grow our business may also be adversely affected.

In the three months ended December 31, 2016 and 2015, we derived 46% and 44% of our revenue from customers located outside of the United States, respectively, and for each of the fiscal years ended December 31, 20162017 and 2015,2016, we derived 46%47% and 44%46% of our revenue from customers located outside of the United States, respectively. We are continuing to expand our international operations as part of our growth strategy. We currently have sales personnel and sales and product support operations in the United States and certain countries across North America, Europe, Australia, Asia, and South America. Our sales organization outside the United States is substantially smaller than our sales organization in the United States and toTo date a very limited portion of our sales has been driven by resellers or other channel partners. We believe our ability to convince new customers to subscribe to our products or to convince existing customers to renew or expand their use of our products is directly correlated to the level of engagement we obtain with the customer. To the extent we are unable to effectively engage with non-U.S. customers due to our limited sales force capacity and limited channel partners, we may be unable to effectively grow in international markets.

We are subject to U.S. export controls, and we incorporate encryption technology into our products that is enabled through mobile applications and other software we may be deemed to export. These encryption products and the underlying technology may be exported outside of the U.S. only with the required export authorizations, including by license, a license exception, or other appropriate government authorizations, including the filing of an encryption registration. We previously deployed mobile applications prior to obtaining the required export authorizations. Accordingly, we have not fully complied with applicable encryption controls in U.S. export administration regulations.

We generally recognize subscription revenue from customers ratably over the terms of their contracts and a majority of our revenue is derived from subscriptions that have terms longer than one month. As a result, a portion of the revenue we report in each quarter is derived from the recognition of deferred revenue relating to subscriptions entered into during previous quarters. Consequently, a decline in new or renewed subscriptions with terms that are longer than one month in any single quarter may have a small impact on our revenue results for that quarter. However, such a decline will negatively affect our revenue in future quarters. Accordingly, the effect of significant downturns in sales and market acceptance of our products, and potential changes in our pricing policies or rate of expansion or retention, may not be fully reflected in our results of operations until future periods. We may also be unable to reduce our cost structure in line with a significant deterioration in sales. In addition, because we believe a substantial percentage of subscriptions to our products are shorter than many comparable SaaS companies and because we have many variations of billing cycles, our deferred revenue may be a less meaningful indicator of our future financial results as compared to other SaaS companies. A significant majority of our costs are expensed as incurred, while revenue is recognized over the life of the agreement with the applicable customer. As a result, increased growth in the number of our customers could continue to result in our recognition of more costs than revenue in the earlier periods of the terms of our agreements. Our subscription model also makes it difficult for us to rapidly increase our revenue through additional sales in any period, as revenue from new customers must be recognized over the applicable subscription term.

We have made and will continue to make substantial expenditures for third-party managed hosting services and investments in our self-managed colocation data centers and expenditures for third-party managed hosting services to support our growth and provide enhanced levels of service to our customers. We recently decreased the amount of capital expenditures on hosting equipment for use in our self-managed colocation data centers as we transition to greater dependence on third-party managed hosting services, but expect to continue to incur significant expense to operate and maintain our self-managed colocation data centers. We employhave employed a hybrid hosting model in which we utilize managed hosting services, where a third party manages most aspects of our hosting operations, and self-managed colocation data centers, where we have more direct control over the hosting infrastructure and its operation. This has and may continue to have a negative impact on our cash flows and gross profit. If costs associated with third-party managed hosting services utilized to support our growth are greater than expected or if we are required to make larger investments in our self-managed colocation data centers than we anticipated, or if costs associated with managed hosting services utilized to support our growth are greater than expected, the negative impact on our operating results would likely exceed our initial expectations. Furthermore, if we determine to no longer utilize our self-managed colocation data centers, we may be forced to accelerate expense recognition as a result of the shorter estimated life of such assets.

We depend on, and anticipate that we will continue to depend on, various third-party relationships in order to sustain and grow our business. We are highly dependent upon third-party technology partners for certain critical features and functionality of our platform. For example, the features available on Zendesk Talk are highly dependent on our technology integration with Twilio, Inc. Failure of this or any other technology provider to maintain, support, or secure its technology platforms in general, and our integrations in particular, or errors or defects in its technology, could materially and adversely impact our relationship with our customers, damage our reputation and brand, and harm our business and operating results. Any loss of the right to use any of this hardware or software could result in delays or difficulties in our ability to provide our products until equivalent technology is either developed by us or, if available, identified, obtained, and integrated.

Our products must integrate with a variety of network, hardware, and software platforms, and we need to continuously modify and enhance our products to adapt to changes in cloud-enabled hardware, software, networking, browser, and database technologies. In particular, we have developed our products to be able to easily integrate with third-party SaaS applications, including the applications of software providers that compete with us, through the interaction of application platform interfaces, or APIs. To date, we have not typically relied on a long-term written contract to govern our relationship with these providers. Instead, we are typically subject to the standard terms and conditions for application developers of such providers, which govern the distribution, operation, and fees of such software systems, and which are subject to change by such providers from time to time. To the extent that we do not have long-term written contracts to govern our relationship with these providers, we rely on the fact that the providers of such software systems continue to allow us access to their APIs to enable these customer integrations. Our business may be harmed if any provider of such software systems:

We may evaluate and consider potential strategic transactions, including acquisitions of, or investments in, businesses, technologies, services, products, and other assets in the future. We also may enter into relationships with other businesses to expand our products and services, which could involve preferred or exclusive licenses, additional channels of distribution, discount pricing, or investments in other companies.

Personal privacy and data security have become significant issues in the United States, Europe, and in many other jurisdictions where we offer our products. The regulatory framework for privacy and security issues worldwide is rapidly evolving and is likely to remain uncertain for the foreseeable future. Many federal, state, and foreign government bodies and agencies have adopted, or are considering adopting, laws and regulations regarding the collection, use, and disclosure of personal information. In the United States, these include rules and regulations promulgated under the authority of federal

There is considerable patent and other intellectual property development activity in our industry. Our future success depends in part on not infringing upon the intellectual property rights of others. From time to time, our competitors or other third parties may claim that we are infringing upon their intellectual property rights, and we may be found to be infringing upon such rights. We may receive claims from third parties, including our competitors, that our products and underlying technology infringe or violate a third party’s intellectual property rights, and we may be found to be infringing upon such rights. We may be unaware of the intellectual property rights of others that may cover some or all of our technology. Any claims or litigation could cause us to incur significant expenses and, if successfully asserted against us, could require that we pay substantial damages or ongoing royalty payments, prevent us from offering one or more of our products, or require that we comply with other unfavorable terms. We may also be obligated to indemnify our customers or business partners in connection with any such litigation and to obtain licenses, modify our products, or refund subscription fees, which could further exhaust our resources. In addition, we may incur substantial costs to resolve claims or litigation, whether or not successfully asserted against us, which could include payment of significant settlement, royalty, or license fees, modification of our products, or refunds to customers of subscription fees. Even if we were to prevail in the event of claims or litigation against us, any claim or litigation regarding our intellectual property could be costly and time-consuming and divert the attention of our management and other employees from our business operations. Such disputes could also disrupt our products, adversely impacting our customer satisfaction and ability to attract customers.

Our agreements with customers and other third parties may include indemnification or other provisions under which we agree to indemnify or otherwise be liable to them for losses suffered or incurred as a result of claims of intellectual property infringement, damages caused by us to property or persons, or other liabilities relating to or arising from our products or other acts or omissions. The term of these contractual provisions often survives termination or expiration of the applicable agreement. Large indemnity payments or damage claims from contractual breach could harm our business, operating results, and financial condition. From time to time, customers require us to indemnify or otherwise be liable to them for breach of confidentiality or failure to implement adequate security measures with respect to their data stored, transmitted, or processed by our products and customer service platform. Although we normally contractually limit our liability with respect to such obligations, we may still incur substantial liability related to them. Any dispute with a customer with respect to such obligations could have adverse effects on our relationship with that customer and other current and prospective customers, reduce demand for our products, and harm our business and operating results.

We use open source software in our products and expect to continue to use open source software in the future. We may face claims from others claiming ownership of, or seeking to enforce the terms of, an open source license, including by demanding release of the open source software, derivative works, or our proprietary source code that was developed using such software. These claims could also result in litigation, require us to purchase a costly license, or require us to devote additional research and development resources to change our products, any of which would have a negative effect on our business and operating results. In addition, if the license terms for the open source software we utilize change, we may be forced to reengineer our products or incur additional costs. Although we have implemented policies to regulate the use and incorporation of open source software into our products, we cannot be certain that we have not incorporated open source software in our products in a manner that is inconsistent with such policies.

Our success and ability to compete depend in part upon our intellectual property. We currently have two issued patents and have a limited number of patent applications, none of which may result in an issued patent. We primarily rely on copyright, trade secret, and trademark laws, trade secret protection, and confidentiality or license agreements with our employees, customers, partners, and others to protect our intellectual property rights. However, the steps we take to protect our intellectual property rights may be inadequate.

We have funded our operations since inception primarily through sales of equity securities, capital lease arrangements, loans for equipment, and subscription payments by our customers for use of our products. We do not know when or if our operations will generate sufficient cash to fund our ongoing operations. In the future, we may require additional capital to respond to business opportunities, challenges, acquisitions, a decline in the level of subscriptions for our products, or unforeseen circumstances. We may not be able to timely secure additional debt or equity financing on favorable terms, or at all. Any debt financing obtained by us could involve restrictive covenants relating to financial and operational matters, which may make it more difficult for us to obtain additional capital and to pursue business opportunities, including potential acquisitions. Additionally, we may not be able to generate sufficient cash to service any debt financing obtained by us, which may force us to reduce or delay capital expenditures or sell assets or operations. If we raise additional funds through further issuances of equity, convertible debt securities, or other securities convertible into equity, our existing stockholders could suffer significant dilution in their percentage ownership of our company, and any new equity securities we issue could have rights, preferences, and privileges senior to those of holders of our common stock. If we are unable to obtain adequate financing or financing on terms satisfactory to us, when we require it, our ability to continue to grow or support our business and to respond to business challenges could be significantly limited.

Our international subsidiaries maintain net assets that are denominated in currencies other than the functional operating currencies of these entities. Accordingly, changes in the value of foreign currencies relative to the U.S. dollar can affect our operating results due to transactional and translational remeasurements that are reflected in our results of operations. To the extent that fluctuations in foreign currency exchange rates cause our results of operations to differ from our expectations or the expectations of our investors, the trading price of our common stock could be adversely affected.

We do not collect sales and use, value added, or similar taxes in all jurisdictions in which we have sales, based on our understanding that such taxes are not applicable. Sales and use, value added, and similar tax laws and rates vary greatly by jurisdiction. Certain jurisdictions in which we do not collect such taxes may assert that such taxes are applicable, which could result in tax assessments, penalties, and interest, and we may be required to collect such taxes in the future. Such tax assessments, penalties, and interest, or future requirements may adversely affect our results of operations.

We review our intangible assets for impairment when events or changes in circumstances indicate the carrying value may not be recoverable. Goodwill is required to be tested for impairment at least annually. As of December 31, 2016,2017, we had a totalnet balance of $53.3$67.0 million of goodwill and intangible assets related to prior acquisitions. An adverse change in market conditions, particularly a change resulting in a significant decrease in our share price, or if such change has the effect of changing one of our critical assumptions or estimates, could result in a change to the estimation of fair value that could result in an impairment charge to our goodwill or intangible assets. Any such charges may have a material negative impact on our operating results.

As of December 31, 2016,2017, we had federal and state net operating loss carryforwards, or NOLs, of $342.9$464.5 million and $145.8$218.4 million, respectively, due to prior period losses. In general, under Section 382 of the Internal Revenue Code of 1986, as amended, or the Code, a corporation that undergoes an “ownership change” is subject to limitations on its ability to utilize its NOLs to offset future taxable income. Our existing NOLs may be subject to limitations arising from previous ownership changes, including in connection with our initial public offering or our follow-on public offering. Future changes in our stock ownership, some of which are outside of our control, could result in an ownership change under Section 382 of the Code. Furthermore, our ability to utilize NOLs of companies that we may acquire in the future may be subject to limitations. There is also a risk that due to regulatory changes, such as suspensions on the use of NOLs, or other unforeseen reasons, our existing NOLs could expire or otherwise be unavailable to offset future income tax liabilities. In addition, under the Tax Cuts and Jobs Act, or the Tax Act, the amount of NOLs that we are permitted to deduct in any taxable year is limited to 80% of our taxable income in such year, where taxable income is determined without regard to the NOL deduction itself. There is a risk that due to changes under the Tax Act, regulatory changes, or other unforeseen reasons, our existing NOLs could expire or otherwise be unavailable to offset future income tax liabilities. For these reasons, we may not be able to realize a tax benefit from the use of our NOLs, whether or not we attain profitability.

Market opportunity estimates and growth forecasts are subject to significant uncertainty and are based on assumptions and estimates that may not prove to be accurate. Our estimates and forecasts relating to the size and expected growth of the customer relationship management market may prove to be inaccurate. Even if the market in which we compete meets our size estimates and forecasted growth, our business could fail to grow at similar rates, if at all.

We rely heavily on hosted SaaS applications from third parties in order to operate critical functions of our business, including billing and order management, enterprise resource planning, and financial accounting services. If these services become unavailable due to extended outages or interruptions, or because they are no longer available on commercially reasonable terms, our expenses could increase, our ability to manage finances could be interrupted and our processes for managing sales of our platformproducts and supporting our customers could be impaired until equivalent services, if available, are identified, obtained, and implemented, all of which could adversely affect our business.

The future success of our business depends upon the continued use of the Internet as a primary medium for commerce, communication, and business applications. Federal, state, or foreign government bodies or agencies have in the past adopted, and may in the future adopt, laws or regulations affecting the use of the Internet as a commercial medium. Changes in these laws or regulations could require us to modify our products in order to comply with these changes or substantially increase costs associated with the operation of our products. Additionally, the adoption of any laws, regulations, or practices limiting

Our corporate headquarters are located in San Francisco, California and we operate in or utilize data centershosting services that are located in North America, Europe, Asia and Asia.Australia. Key features and functionality of our products are enabled by third parties that are headquartered in California and operate in or utilize data centers in the United States and Europe. Additionally, we rely on our network and third-party infrastructure and enterprise applications, internal technology systems, and our website for our development, marketing, operational support, hosted services, and sales activities. In the event of a major earthquake, hurricane, or catastrophic event such as fire, flood, power loss, telecommunications failure, cyber-attack, war, or terrorist attack, we may be unable to continue our operations and may endure system interruptions, reputational harm, delays in our application development, lengthy interruptions in our products, breaches of data security, and loss of critical data, all of which could have an adverse effect on our future operating results.

The outcome of the referendum has also created uncertainty with regard to the regulation of data protection in the United Kingdom. In particular, it is unclear how the United Kingdom's vote to leave the European Union will affect the United Kingdom's enactment of the European General Data Protection Regulation, and how data transfers to and from the United Kingdom will be regulated.

The trading price of our common stock has been, and may continue to be, volatile and could fluctuate widely regardless of our operating performance. The market price of our common stock may fluctuate significantly in response to numerous factors, many of which are beyond our control, including:

As of December 31, 2016,2017, our directors, officers, five percent or greater stockholders, and their respective affiliates beneficially owned in the aggregate approximately 32.5%41% of our outstanding common stock. As a result, these stockholders have the ability to influence us through this ownership position. These stockholders may be able to exert significant influence in matters requiring stockholder approval. For example, these stockholders may be able to exert significant influence in elections of directors, amendments of our organizational documents, and approval of any merger, sale of assets, or other major corporate transaction. This may prevent or discourage unsolicited acquisition proposals or offers for our common stock that you may feel are in your best interest as one of our stockholders.

The market price of our common stock could decline as a result of substantial sales of our common stock, particularly sales by our directors, executive officers, and significant stockholders, or the perception in the market that holders of a large number of shares intend to sell their shares.

Provisions in our certificate of incorporation and bylaws may have the effect of delaying or preventing a change of control or changes in our management. Our certificate of incorporation and bylaws include provisions that:

As a public company, we are subject to the reporting requirements of the Exchange Act, the Sarbanes-Oxley Act, the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010, the listing requirements of the exchanges and other markets upon which our common stock is listed, and other applicable securities rules and regulations. Compliance with these rules and regulations increase our legal and financial compliance costs, make some activities more difficult, time-consuming, or costly, and increase demand on our systems and resources. The Exchange Act requires, among other things, that we file annual, quarterly, and current reports with respect to our business and operating results. 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, if required, improve our disclosure controls and procedures and internal control over financial reporting to meet this standard, significant resources and management oversight may be required. We are required to disclose changes made in our internal control and procedures on a quarterly basis and to furnish a report by management on, among other things, the effectiveness of our internal control over financial reporting. As a result of the complexity involved in complying with the rules and regulations applicable to public companies, our management’s attention may be diverted from other business concerns, which could adversely affect our business and operating results. Although we have already hired additional employees to assist us in complying with these requirements, we may need to hire more employees in the future or engage outside consultants, which will increase our operating expenses.

We have never declared or paid any cash dividends on our common stock. We currently anticipate that we will retain future earnings for the development, operation, and expansion of our business, and do not anticipate declaring or paying any cash dividends for the foreseeable future. In addition, our ability to pay cash dividends on our common stock may be prohibited or limited by the terms of our future debt financing arrangements. Any return to stockholders will therefore be limited to the increase, if any, of our stock price, which may never occur.

The trading market for our common stock depends in part on the research and reports that securities or industry analysts publish about us or our business. If one or more of the analysts who cover us downgrade our common stock or publish inaccurate or unfavorable research about our business, our common stock price would likely decline. If one or more of these analysts cease coverage of us or fail to publish reports on us regularly, demand for our common stock could decrease, which might cause our common stock price and trading volume to decline.

Our certificate of incorporation and bylaws provide that, unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware shall be the sole and exclusive forum for (A) any derivative action or proceeding brought on our behalf, (B) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers, or other employees to us or our stockholders, (C) any action asserting a claim arising pursuant to any provision of the General Corporation Law of the State of Delaware, our certificate of incorporation, or our bylaws, or (D) any action asserting a claim against us governed by the internal affairs doctrine. Any person or entity purchasing or otherwise acquiring any interest in shares of our capital stock shall be deemed to have notice of and consented to the provisions of our certificate of incorporation described above. This choice of forum provision may limit a stockholder’s ability to bring a claim in a judicial forum that it finds favorable for disputes with us or our directors, officers, or other employees, which may discourage such lawsuits against us and our directors, officers, and other employees. Alternatively, if a court were to find these provisions of our certificate of incorporation inapplicable to, or unenforceable in respect of, one or more of the specified types of actions or proceedings, we may incur additional costs associated with resolving such matters in other jurisdictions, which could adversely affect our business, financial condition, or results of operations.

None.

Our corporate headquarters are located in San Francisco, California. We operate in San Francisco under threefour leases for approximately 72,900, 52,000, 34,900, and 18,000 square feet of space, respectively. These leases expire in August 2022, October 2023, October 2019, and January 2021, respectively.

From time to time, we may be subject to legal proceedings, claims, investigations, and government inquires in the ordinary course of business. We have received, and may in the future continue to receive, claims from third parties asserting, among other things, infringement of their intellectual property rights, defamation, privacy, and contractual rights. Legal risk is enhanced in certain jurisdictions outside the United States where our protection from liability for content added to our products 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 to defend ourselves, our partners, and our customers by determining the scope, enforceability, and validity of third-party proprietary rights, or to establish our proprietary rights. The results of any current or future litigation cannot be predicted with certainty, and regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs, diversion of management resources, and other factors.

Not Applicable.

Our common stock has been listed on the New York Stock Exchange under the symbol “ZEN” since May 15, 2014, the date of our initial public offering.  

As of December 31, 2016,2017, there were approximately 4538 holders of record of our common stock. However, because many of our shares of common stock are held by brokers and other institutions on behalf of stockholders, we are unable to accurately estimate the total number of stockholders represented by these record holders.

We have never declared or paid any cash dividend on our capital stock. We currently 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, operating results, capital requirements, contractual restrictions, general business conditions, and other factors that our board of directors may deem relevant.

No shares of our common stock were repurchased during the three months ended December 31, 2016.2017.

See Item 12, “Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters” for information regarding securities authorized for issuance.

The consolidated statements of operations data and the consolidated balance sheets data are derived from our audited consolidated financial statements and should be read together with “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” our consolidated financial statements, and the related notes included elsewhere in this Annual Report on Form 10-K.  Our historical data results are not necessarily indicative of our results in any future period.

We derive substantially all of our revenue from subscription services, which are comprised of subscription fees from customer accounts on Zendesk Support and, to a lesser extent, Chat, Talk and Talk.Guide. Each subscription may have multiple authorized users, and we refer to each user as an “agent.” The number of agents ranges from one to thousands for various customer accounts. Our pricing is generally established on a per agent basis. We offer a range of subscription account plans for our products that vary in price based on functionality, type and, for Zendesk Support and Chat, the amount of product support we offer. We also offer a range of additional features that customers can purchase and add to their subscriptions. Certain arrangements provide for incremental fees above a fixed maximum number of monthly agents during the subscription term. We sell subscription services under contractual agreements that vary in length, ranging between one month and multiple years, with the majority of subscriptions having a term of either one month or one year.

We intend to continue to invest additional resources in our infrastructure, product support, and professional service organizations, organically and through acquisitions and organically.acquisitions. We expect that recent and future business acquisitions will result in increased amortization expense of intangible assets such as acquired technology. As we continue to invest in technology innovation, we expect to continue to incur capitalized internal-use software costs and related amortization. We expect these investments in technology to not only expand the capabilities of our products but also to increase the efficiency of how we deliver these services, enabling us to improve our gross margin over time. The level and timing of investment in these areas could affecttime, although our cost of revenuegross margin may decrease in the future.near-term and may vary from period to period as our revenue fluctuates and as result of the timing and amount of these investments. To the extent that we continue to rely on third-party technology to provide certain functionality within our products or for certain subscription plans or integrations, we expect third-party license fees for technology that is incorporated in such products and subscription plans to remain significant over time.

Other income (expense), net consists primarily of interest income from marketable securities and foreign currency gains and losses, offset by interest expense associated with our credit facility (terminated in June 2015).losses.

Provision for (benefit from) income taxes consists of federal and state income taxes in the United States and income taxes in certain foreign jurisdictions.

Our quarterly revenue increased sequentially for each period presented, primarily due to sales of new subscriptions to our products and net expansion by our existing customers. We cannot assure you that this pattern of sequential growth in revenue will continue.

Our quarterly costs and expenses increased sequentially for each period presented, primarily due to increased compensation-related costs related to an increase in headcount in connection with the expansion of our business.

Our largest source of operating cash inflows is cash collections from our customers. Our primary uses of cash from operating activities are for employee-related expenditures, marketing programs, hosting costs, and third-party hosting costs.rent for office space.

Net cash provided by operatingused in investing activities in 20142017 of $69.9 million was $2.1 million, reflecting our net loss of $67.4 million, adjusted by non-cash charges including share-based compensation expense of $32.1 million, depreciation and amortization expense of $11.5 million, and changes in our working capital. The changes in our working capital were primarily attributable to an increase in deferred revenuepurchases of $22.4marketable securities of $29.5 million, duenet of sales and maturities, cash paid for the acquisition of Outbound Solutions, Inc., or Outbound, net of cash acquired, of $16.5 million, purchases of property and equipment of $16.4 million primarily associated with leasehold improvements for newly leased office facilities and hosting equipment to maintain our self-managed colocation data centers, and capitalized internal-use software costs of $7.5 million related to the growthdevelopment of additional features and functionality for our subscription services, an increase in accrued compensation liabilities of $5.8 million primarily due to a significant increase in headcount and timing of payments, an increase in other assets and liabilities of $1.7 million due to increased deferred rent, and an increase in accounts payable and accrued liabilities of $1.3 million due to timing of payments and a higher level of expenses consistent with the overall growth of our business. These sources of cash were partially offset by an increase in accounts receivable of $3.8 million due to the growth of our business and the timing of customer billings and collections and an increase in prepaid expenses and other current assets of $1.4 million.

Net cash used in investingprovided by financing activities in 20142017 of $71.3$43.1 million was primarily attributable to purchasesproceeds from exercises of marketable securitiesemployee stock options of $39.9$31.9 million netand proceeds from our employee stock purchase plan of sales and maturities, purchases of property and equipment of $21.7 million primarily associated with leasehold improvements for newly leased office facilities and hosting equipment, and capitalized internal-use software costs of $8.0 million associated with the development of additional features and functionality for our products.

Net cash provided by financing activities in 2016 of $35.6 million was primarily attributable to proceeds from the exerciseexercises of employee stock options of $25.4 million and proceeds from our employee stock purchase plan of $11.0 million.