twtr-10k_20151231.htm

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. YES x 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 x

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 x NO ¨

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

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

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

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

The aggregate market value of the voting and non-voting common equity held by non-affiliates of the registrant, based on the closing price of a share of the registrant’s common stock on June 30, 2015 as reported by the New York Stock Exchange on such date was approximately $21,559,514,818. Shares of the registrant’s common stock held by each executive officer, director and holder of 5% or more of the outstanding common stock have been excluded in that such persons may be deemed to be affiliates. This calculation does not reflect a determination that certain persons are affiliates of the registrant for any other purpose.

The number of shares of the registrant’s common stock outstanding as of February 17, 2016 was 697,726,321.

Portions of the registrant’s Definitive Proxy Statement relating to the Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s fiscal year ended December 31, 2015.

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.

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

The numbers of active users presented in this Annual Report on Form 10-K are based on internal company data. While these numbers are based on what we believe to be reasonable estimates for the applicable period of measurement, there are inherent challenges in measuring usage and user engagement across our large user base around the world. For example, there are a number of false or spam accounts in existence on our platform. We have performed an internal review of a sample of accounts and estimate that false or spam accounts represented less than 5% of our MAUs as of December 31, 2014. In making this determination, we applied significant judgment, so our estimation of false or spam accounts may not accurately represent the actual number of such accounts, and the actual number of false or spam accounts could be higher than we have estimated. We are continually seeking to improve our ability to estimate the total number of spam accounts and eliminate them from the calculation of our active users, and in the past have made improvements in our spam detection capabilities that have resulted in the suspension of a large number of accounts. Spam accounts that we have identified are not included in the active user numbers presented in this Annual Report on Form 10-K. We treat multiple accounts held by a single person or organization as multiple users for purposes of calculating our active users because we permit people and organizations to have more than one account. Additionally, some accounts used by organizations are used by many people within the organization. As such, the calculations of our active users may not accurately reflect the actual number of people or organizations using our platform.

Our metrics are also affected by applications that automatically contact our servers for regular updates with no discernible user action involved, and this activity can cause our system to count the users associated with such applications as active users on the day or days such contact occurs. In the three months ended December 31, 2014, approximately 8.5% of users used third party applications that may have automatically contacted our servers for regular updates without any discernible additional user-initiated action. As such, the calculations of MAUs presented in this Annual Report on Form 10-K may be affected as a result of this activity.

In addition, our data regarding user geographic location for purposes of reporting the geographic location of our MAUs is based on the IP address or phone number associated with the account when a user initially registered the account on Twitter. The IP address or phone number may not always accurately reflect a user’s actual location at the time such user engaged with our platform.

We regularly review and may adjust our processes for calculating our internal metrics to improve their accuracy. Our measures of user growth and user engagement may differ from estimates published by third parties or from similarly-titled metrics of our competitors due to differences in methodology. We present and discuss our total audience based on both internal metrics and relying on data from Google Analytics, which measures logged-out visitors to our properties.

Twitter gives everyone the power to create and share ideas and information instantly without barriers. Our service is live—live commentary, live connections, live conversations. Whether it is breaking news, entertainment, sports, or everyday topics, hearing about and watching a live event unfold is the fastest way to understand the power of Twitter. Twitter has always been considered a "second screen" for what is happening in the world and we believe we can become the first screen for everything that is happening now. And by doing so, we believe we can build the planet’s largest daily connected audience.

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

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

Periscope and Vine. Our mobile application, Periscope, lets anyone broadcast and watch video live with others. We recently added the ability to broadcast from a GoPro camera, and to watch any broadcast live from a Tweet. Pairing Periscope with Twitter gives broadcasters greater distribution (anywhere a Tweet can be displayed, a Periscope can too) and the ability to integrate into our revenue products. Vine is a mobile application that enables users to create and distribute short looping videos of up to six seconds in length. We do not currently monetize videos on Periscope or Vine, other than to the extent they can be integrated into our revenue products.

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

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

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

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

We provide a set of tools, public APIs and embeddable widgets that developers can use to contribute their content to our platform, syndicate and distribute Twitter content across their properties and enhance their websites and applications with Twitter content. Websites integrating with Twitter add value to our user experience. Indeed 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. The goal of our platform product development is to make it easy for developers to integrate seamlessly with Twitter.

Our Fabric platform offers lightweight modular software development kits that help developers build more stable applications, gives them mobile analytics, the ability to generate revenue through Twitter’s mobile-focused advertising exchange, MoPub, and allows them to tap into Twitter’s sign-in systems for simpler identity verification. Fabric also provides a simple way for developers to incorporate real-time Twitter content for greater syndication.

We offer subscription access to our public data feed for partners who wish to access data beyond our public API, which offers a limited amount of our public data for free. Our “Gnip” branded products and services offer more sophisticated data sets and better data enrichments to allow developers and businesses to utilize our public content to derive business insights and build products using the unique content that is shared on Twitter.

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

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.

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

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

We have a global sales force and sales support staff that is focused on attracting and retaining advertisers. Our sales force and sales support staff assists 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. Our advertisers also use our self-serve advertising platform to launch and manage their advertising campaigns.

Since our inception, our user base has grown primarily by word-of-mouth. Historically, we have built our brand through these efforts and increased usage of Twitter worldwide with relatively minimal marketing costs. However, we began to spend more on sales and marketing in 2015 than we have had historically, and expect our sales and marketing expense to continue to increase in absolute dollars in 2016.

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

As of December 31, 2015, we had 990 issued patents in the United States and foreign countries relating to message distribution, graphical user interfaces, security and related technologies. Our issued United States patents are expected to expire between 2016 and 2033.

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

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

The IPA limits our ability to prevent infringement of our patents. See the section titled “Risk Factors—Our intellectual property rights are valuable, and any inability to protect them could reduce the value of our products, services and brand” for a further discussion of the IPA.

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

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

We are also subject to federal, state and foreign laws regarding privacy and the protection of user data. Foreign data protection, privacy, consumer protection, content regulation and other laws and regulations are often more restrictive than those in the United States. There are also a number of legislative proposals pending before the U.S. Congress, various state legislative bodies and foreign governments concerning data protection that could affect us. For example, regulation relating to the 1995 European Union Data Protection Directive is currently being considered by European legislative bodies that may include more stringent operational requirements for entities processing personal information and significant penalties for non-compliance.

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

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

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

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

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

We broadcast via Periscope and/or 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 intends to continue to use, our investor relations website, as well as certain Twitter accounts (@jack, @twitter and @twitterIR), as means of disclosing material non-public information and for complying with its 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.

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

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

The size of our user base and our users’ level of engagement are critical to our success. We had 320 million average MAUs in the three months ended December 31, 2015, representing a 9% increase from 292 million average MAUs in the three months ended December 31, 2014, and flat versus the three months ended September 30, 2015. In the three months ended December 31, 2015, MAUs, excluding SMS Fast Followers, grew 6% year-over-year to 305 million, but were down on a sequential basis for the three months ended September 30, 2015. Our financial performance has been and will continue to be significantly determined by our success in growing the number of users and increasing their overall level of engagement on our platform as well as the number of ad engagements. We anticipate that our user growth rate will slow over time as the size of our user base increases. For example, in general, a higher proportion of Internet users in the United States uses Twitter than Internet users in other countries and, in the future, we expect our user growth rate in certain international markets, such as Argentina, Brazil, France, India, Japan and the Philippines, to continue to be higher than our user growth rate in the United States. To the extent our logged-in user growth rate slows, our success will become increasingly dependent on our ability to increase levels of ad engagement on Twitter, and monetizing our total audience on logged-out usage and syndicated properties as well as increasing revenue growth from the sale to advertisers of our advertising products which we place on third party publishers’ websites, applications and other offerings. We generate a substantial majority of our revenue based upon engagement by our users with the ads that we display. If people do not perceive our products and services to be useful, reliable and trustworthy, we may not be able to attract users or increase the frequency of their engagement with our platform and the ads that we display. A number of consumer-oriented websites that achieved early popularity have since seen their user bases or levels of engagement decline, in some cases precipitously. There is no guarantee that we will not experience a similar erosion of our user base or engagement levels. A number of factors could potentially negatively affect user growth and engagement, including if:

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

If our users do not continue to contribute content or their contributions are not valuable to other users, we may experience a decline in the number of users accessing our products and services and user engagement, which could result in the loss of advertisers, platform partners and revenue.

Our success depends on our ability to provide users of our products and services with valuable content, which in turn depends on the content contributed by our users. We believe that one of our competitive advantages is the quality, quantity and real-time nature of the content on Twitter, and that access to unique or real-time content is one of the main reasons users visit Twitter. Our ability to expand into new international markets depends on the availability of relevant local content in those markets. We seek to foster a broad and engaged user community, and we encourage world leaders, government officials, celebrities, athletes, journalists, sports teams, media outlets and brands to use our products and services to express their views to broad audiences. We also encourage media outlets to use our products and services to distribute their content. If users, including influential users, do not continue to contribute content to Twitter, and we are unable to provide users with valuable and timely content, our user base and user engagement may decline. Additionally, if we are not able to address user concerns regarding the safety and security of our products and services or if we are unable to successfully prevent abusive or other hostile behavior on our platform, the size of our user base and user engagement may decline. We rely on the sale of advertising services for the substantial majority of our revenue. If we experience a decline in the number of users, user growth rate, or user engagement, including as a result of the loss of world leaders, government officials, celebrities, athletes, journalists, sports teams, media outlets and brands who generate content on Twitter, advertisers may not view our products and services as attractive for their marketing expenditures, and may reduce their spending with us which would harm our business and operating results.

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

The substantial majority of our revenue is currently generated from third parties advertising on Twitter. We generated approximately 90% of our revenue from advertising in each of the fiscal years ended December 31, 2014 and 2015. We generate substantially all of our advertising revenue through the sale of our three Promoted Products: Promoted Tweets, Promoted Accounts and Promoted Trends. As is common in our industry, our advertisers do not have long-term advertising commitments with us. In addition, many of our advertisers purchase our advertising services through one of several large advertising agency holding companies. Advertising agencies and potential new advertisers may view our Promoted Products as experimental and unproven, and we may need to devote additional time and resources to educate them about our products and services. Advertisers also may choose to reach users through our free products and services, instead of our Promoted Products. Advertisers will not continue to do business with us, or they will reduce the prices they are willing to pay to advertise with us, if we do not deliver ads in an effective manner, or if they do not believe that their investment in advertising with us will generate a competitive return relative to alternatives, including online, mobile and traditional advertising platforms. Additionally, since our initial public offering, our revenue growth has been primarily driven by increases in the number of our users and increases in our ad load driven by strong advertiser demand as well as other factors. To date, our available advertising inventory has been greater than demand. Our future revenue growth, however, may be limited on certain days by available advertising inventory for specific ad types if we do not increase the number of our users, their engagement or monetize our larger global audience. Our advertising revenue could be adversely affected by a number of other factors, including:

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

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

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

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

We also face significant competition for advertiser spend. The substantial majority of our revenue is currently generated through third parties advertising on Twitter, and we compete against online and mobile businesses, including those referenced above, and traditional media outlets, such as television, radio and print, for advertising budgets. We also compete with advertising networks, exchanges, demand side platforms and other platforms, such as Google AdSense, DoubleClick Ad Exchange, Yahoo Ad Exchange, AOL’s Ad.com and Microsoft Media Network, for marketing budgets and in the development of the tools and systems for managing and optimizing advertising campaigns. In order to grow our revenue and improve our operating results, we must increase our share of spending on advertising relative to our competitors, many of which are larger companies that offer more traditional and widely accepted advertising products. In addition, some of our larger competitors have substantially broader product or service offerings and leverage their relationships based on other products or services to gain additional share of advertising budgets.

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

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

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

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

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

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

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

We depend on highly skilled personnel to grow and operate our business, and if we are unable to hire, retain and motivate our personnel, we may not be able to grow effectively.

Our future success will depend upon our continued ability to identify, hire, develop, motivate and retain highly skilled personnel, including senior management, engineers, designers and product managers. Our ability to execute efficiently is dependent upon contributions from our employees, in particular our senior management team. We do not have employment agreements other than offer letters with any member of our senior management or other key employee, and we do not maintain key person life insurance for any employee. In addition, from time to time, there may be changes in our senior management team that may be disruptive to our business. If our senior management team, including any new hires that we may make, fails to work together effectively and to execute our plans and strategies on a timely basis, our business could be harmed.

Our growth strategy also depends on our ability to attract and retain highly skilled personnel. Identifying, recruiting, training and integrating qualified individuals will require significant time, expense and attention. In addition to hiring new employees, we must continue to focus on retaining our best employees. Because of our initial public offering, many of our employees are able to receive significant proceeds from sales of our equity in the public markets, which may reduce their motivation to continue to work for us. Competition for highly skilled personnel is intense, particularly in the San Francisco Bay Area, where our headquarters is located. We may need to invest significant amounts of cash and equity to attract and retain new employees and we may never realize returns on these investments. If we are not able to effectively attract and retain employees, our ability to achieve our strategic objectives will be adversely impacted, and our business will be harmed.

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

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

If our revenue from our international operations, and particularly from our operations in the countries and regions where we have focused our spending, does not exceed the expense of establishing and maintaining these operations, our business and operating results will suffer. In addition, our user base may expand more rapidly in international regions where we are less successful in monetizing our products and services. As our user base continues to expand internationally, we will need to increase revenue from the activity generated by our international users in order to grow our business. For example, users outside the United States constituted 80% of our average MAUs in the three months ended December 31, 2015, but our international revenue, as determined based on the billing location of our advertisers, was only 35% of our consolidated revenue in the three months ended December 31, 2015. Our inability to successfully expand internationally could adversely affect our business, financial condition and operating results.

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

We make our products and services available across a variety of operating systems and through websites. We are dependent on the interoperability of our products and services with popular devices, desktop and mobile operating systems and web browsers that we do not control, such as Mac OS, Windows, Android, iOS, Chrome and Firefox. Any changes in such systems, devices or web browsers that degrade the functionality of our products and services, make it difficult for our users to access our content, limit our ability to target or measure the effectiveness of ads, impose fees related to our products or services or give preferential treatment to competitive products or services could adversely affect usage of our products and services. Further, if the number of platforms for which we develop our product expands, it will result in an increase in our operating expenses. In order to deliver high quality products and services, it is important that our products and services work well with a range of operating systems, networks, devices, web browsers and standards that we do not control. In addition, because a majority of our users access our products and services through mobile devices, we are particularly dependent on the interoperability of our products and services with mobile devices and operating systems. We may not be successful in developing relationships with key participants in the mobile industry or in developing products or services that operate effectively with these operating systems, networks, devices, web browsers and standards. In the event that it is difficult for our users to access and use our products and services, particularly on their mobile devices, our user growth and engagement could be harmed, and our business and operating results could be adversely affected.

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

We have developed a global platform for public self-expression and conversation in real time, and the market for our products and services is relatively new and may not develop as expected, if at all. Despite our efforts to reduce barriers to consumption, people who are not our users may not understand the value of our products and services and new users may initially find our product confusing. There may be a perception that our products and services are only useful to users who tweet, or to influential users with large audiences. Convincing potential and new users of the value of our products and services is critical to increasing our user base and to the success of our business.

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

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

Since our inception, we have incurred significant operating losses, and, as of December 31, 2015, we had an accumulated deficit of $2.09 billion. Although our revenue has grown rapidly, increasing from $28.3 million in 2010 to $2.22 billion in 2015, we expect that our revenue growth rate will slow in the future as a result of a variety of factors, including the decline in the growth rate of our user base. We believe that our future revenue growth will depend on, among other factors, our ability to attract new users, increase user engagement and ad engagement, increase our brand awareness, compete effectively, maximize our sales efforts, demonstrate a positive return on investment for advertisers, successfully develop new products and services and expand internationally. Accordingly, you should not rely on the revenue growth of any prior quarterly or annual period as an indication of our future performance. We also expect our costs to increase in future periods as we continue to expend substantial financial resources on:

These investments may not result in increased revenue or growth in our business. If we are unable to generate adequate revenue growth and to manage our expenses, we may continue to incur significant losses in the future and may not be able to achieve or maintain profitability.

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

We depend on the ability of our users, platform partners and advertisers to access the Internet. Currently, this access is provided by companies that have significant market power in the broadband and Internet access marketplace, including incumbent telephone companies, cable companies, mobile communications companies, government-owned service providers, device manufacturers and operating system providers, any of whom could take actions that degrade, disrupt or increase the cost of user access to our products or services, which would, in turn, negatively impact our business. The adoption 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 2014 and 2015. We also rely on other companies to maintain reliable network systems that provide adequate speed, data capacity and security to us and our users. As the Internet continues to experience growth in the number of users, frequency of use and amount of data transmitted, the Internet infrastructure that we and our users rely on may be unable to support the demands placed upon it. The failure of the Internet infrastructure that we or our users rely on, even for a short period of time, could undermine our operations and harm our operating results.

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

Our ability to increase the size and engagement of our user base, attract platform partners and advertisers and generate revenue will depend in part on our ability to improve existing products and services and create successful new products and services, both independently and in conjunction with third parties. We may introduce significant changes to our existing products and services or develop and introduce new and unproven products and services, including technologies with which we have little or no prior development or operating experience. For example, in 2015, we introduced Periscope, a mobile application that lets users share and experience live video from their mobile phones and in 2013, we introduced Vine, a mobile application that enables users to create and distribute videos that are up to six seconds in length, and #Music, a mobile application that helped users discover new music and artists based on Twitter data profiles which we discontinued in 2014. Also, we recently introduced new features to Twitter such as “Moments”, a curated collection of Tweets, photos, videos, Vines and Periscope broadcasts about current news stories or events; “While You Were Away,” which surfaces Tweets a logged-in user may have missed since last accessing Twitter; and Instant Timeline, which helps create a timeline for new users as well as new features to our Promoted Tweets like promoted video ads. If new or enhanced products, product features or services fail to engage users, platform partners and advertisers, we may fail to attract or retain users or to generate sufficient revenue or operating profit to justify our investments, and our business and operating results could be adversely affected. In addition, we have launched and expect to continue to launch strategic initiatives, such as the Nielsen Twitter TV Rating, that do not directly generate revenue but which we believe will enhance our attractiveness to users, platform partners and advertisers. In the future, we may invest in new products, product features, services and initiatives to generate revenue, but there is no guarantee these approaches will be successful. We may not be successful in future efforts to generate revenue from our new products or services. If our strategic initiatives do not enhance our ability to monetize our existing products and services or enable us to develop new approaches to monetization, we may not be able to maintain or grow our revenue or recover any associated development costs and our operating results could be adversely affected.

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

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

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

We expect to invest in our headcount and operations, which will continue to place significant demands on our management, operational and financial infrastructure. As of December 31, 2015, we had approximately 3,900 full-time employees, an increase of approximately 260 full-time employees since December 31, 2014. We intend to continue to make investments to expand our operations, research and development, sales and marketing and general and administrative organizations, as well as our international operations. We face significant competition for employees, particularly engineers, designers and product managers, from other Internet and high-growth companies, which include both publicly-traded and privately-held companies, and we may not be able to hire new employees quickly enough to meet our needs. To attract highly skilled personnel, we have had to offer, and believe we will need to continue to offer, highly competitive compensation packages. In addition, as we have grown, we have significantly expanded our operating lease commitments. As we continue to evolve, we are subject to the risks of over-hiring, over-compensating our employees and over-expanding our operating infrastructure, and to the challenges of integrating, developing and motivating a rapidly growing employee base in various countries around the world. In addition, we may not be able to innovate or execute as quickly as a smaller, more efficient organization. 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 employee morale, productivity and retention could suffer, and our business and operating results could be adversely affected.

Providing our products and services to our users is costly and we expect our expenses to continue to increase in the future as we broaden our user base and increase user engagement, as users increase the amount of content they contribute, and as we develop and implement new features, products and services that require more infrastructure, such as our mobile video products, Vine and Periscope. In addition, our operating expenses, such as our research and development expenses and sales and marketing expenses, have grown rapidly as we have expanded our business. Historically, our costs have increased each year due to these factors and we expect to continue to incur increasing costs to support our anticipated future growth. We expect to continue to invest in our infrastructure so that we can provide our products and services rapidly and reliably to users around the world, including in countries where we do not expect significant near-term monetization. Continued growth could also strain our ability to maintain reliable service levels for our users and advertisers, develop and improve our operational, financial, legal and management controls, and enhance our reporting systems and procedures. As a public company we incur significant legal, accounting and other expenses that we did not incur as a private company. Our expenses may grow faster than our revenue, and our expenses may be greater than we anticipate. Managing our growth will require significant expenditures and allocation of valuable management resources. If we fail to achieve the necessary level of efficiency in our organization as it grows, our business, operating results and financial condition would be harmed.

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

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

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

One of the reasons people come to Twitter is for real-time information. We have experienced, and may in the future experience, service disruptions, outages and other performance problems due to a variety of factors, including infrastructure changes, human or software errors, hardware failure, capacity constraints due to an overwhelming number of people accessing our products and services simultaneously, computer viruses and denial of service or fraud or security attacks. For instance, in September 2015, we experienced a brief service outage during which Twitter.com was inaccessible as a result, in part, of a software misconfiguration in one of our infrastructure components. Additionally, although we are investing significantly to improve the capacity, capability and reliability of our infrastructure, we are not currently serving traffic equally through our co-located data centers that support our platform. Accordingly, in the event of a significant issue at the data center supporting most of our network traffic, some of our products and services may become inaccessible to the public or the public may experience difficulties accessing our products and services. Any disruption or failure in our infrastructure could hinder our ability to handle existing or increased traffic on our platform, which could significantly harm our business.

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

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

We believe that maintaining and promoting our brand is critical to expanding our base of users, platform partners and advertisers. Maintaining and promoting our brand will depend largely on our ability to continue to provide useful, reliable and innovative products and services, which we may not do successfully. We may introduce new features, products, services or terms of service that users, platform partners or advertisers do not like, which may negatively affect our brand. Additionally, the actions of platform partners may affect our brand if users do not have a positive experience using third-party applications or websites integrated with Twitter or that make use of Twitter content. Our brand may also be negatively affected by the actions of users that are hostile or inappropriate to other people, by users impersonating other people, by users identified as spam, by users introducing excessive amounts of spam on our platform or by third parties obtaining control over users’ accounts. For example, in April 2013, attackers obtained the credentials to the Twitter account of the Associated Press news service through a “phishing” attack targeting Associated Press employees. The attackers posted an erroneous Tweet from the Associated Press account reporting that there had been explosions at the White House, triggering a stock market decline, and focusing media attention on our brand and security efforts. Maintaining and enhancing our brand may require us to make substantial investments and these investments may not achieve the desired goals. If we fail to successfully promote and maintain our brand or if we incur excessive expenses in this effort, our business and operating results could be adversely affected.

We receive a high degree of media coverage around the world. Negative publicity about our company, including about our product quality and reliability, changes to our products and services, privacy and security practices, litigation, regulatory activity, the actions of our users or user experience with our products and services, even if inaccurate, could adversely affect our reputation and the confidence in and the use of our products and services. Such negative publicity could also have an adverse effect on the size, engagement and loyalty of our user base and result in decreased revenue, which could adversely affect our business and operating results.

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

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

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

We believe user engagement with our products and services depends in part on the availability of applications and content generated by platform partners. For instance, in October 2014, we launched Fabric, a platform that offers lightweight modular software development kits that help developers build more stable applications, generate revenue through Twitter’s mobile advertising exchange, MoPub, and tap into Twitter’s sign-in systems for simpler identity verification. If platform partners focus their efforts on other platforms despite these and other efforts, the availability and quality of applications and content for our products and services may suffer. There is no assurance that platform partners will continue to develop and maintain applications and content for our products and services. If platform partners cease to develop and maintain applications and content for our products and services, user engagement may decline. In addition, we generate revenue from licensing our historical and real-time data to third parties. If any of these relationships are terminated or not renewed, or if we are unable to enter into similar relationships in the future, our operating results could be adversely affected.

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

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

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

Our products and services incorporate complex software and we encourage employees to quickly develop and help us launch new and innovative features. Our software, including any open source software that is incorporated into our code, has contained, and may now or in the future contain, errors, bugs or vulnerabilities. For example, in September 2015, we experienced a brief service outage during which Twitter.com was inaccessible as a result, in part, of a software misconfiguration in one of our infrastructure components. Additionally, in February 2016, we discovered, and corrected, a bug that affected our password recovery systems for about 24 hours. Although this issue did not expose passwords or information that could be used directly to access an account, it had the potential to expose the email address and phone number associated with a small number of accounts (less than 10,000 active accounts). Some errors in our software code may only be discovered after the product or service has been released. Any errors, bugs or vulnerabilities discovered in our code after release could result in damage to our reputation, loss of users, loss of platform partners, loss of advertisers or advertising revenue or liability for damages or regulatory inquiries or lawsuits, any of which could adversely affect our business and operating results.

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

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

From time to time, governments, regulators and others have expressed concerns about whether our products, services or practices compromise the privacy of users and others. While we strive to comply with applicable data protection laws and regulations, as well as our own posted privacy policies and other obligations we may have with respect to privacy and data protection, the failure or perceived failure to so comply may result, and in some cases has resulted, in inquiries and other proceedings or actions against us by governments, regulators or others. Moreover, foreign data protection, privacy, consumer protection, content regulation and other laws and regulations are often more restrictive than those in the United States. In particular, the European Union and its member states traditionally have taken broader views as to types of data that are subject to privacy and data protection, and have imposed greater legal obligations on companies in this regard. A number of proposals are pending before federal, state and foreign legislative and regulatory bodies that could significantly affect our business. For example, regulation relating to the 1995 European Union Data Protection Directive is currently being considered by European legislative bodies that may include more stringent operational requirements for entities processing personal information and significant penalties for non-compliance. Additionally, in October 2015, recently the Court of Justice of the European Union invalidated the EU–U.S. Safe Harbor Framework. We rely upon the EU–U.S. Safe Harbor Framework to transfer certain personal information of European Union residents to the United States, and revocation of the Safe Harbor Framework could require us to create duplicative, and potentially expensive, information technology infrastructure and business operations in Europe or limit our ability to collect and use personal information collected in Europe. U.S. and EU authorities reached a political agreement on February 2, 2016 regarding a new potential means for legitimizing personal data transfers from the European Economic Area to the U.S., the EU-U.S. Privacy Shield, but it is unclear whether the EU-U.S. Privacy Shield will be formally implemented and whether the EU-U.S. Privacy Shield, if formally implemented, would include significant data transfer restrictions that could impact our business or result in substantial expense to implement. Any of these could disrupt our business.

Similarly, there have been a number of recent legislative proposals in the United States, at both the federal and state level, that would impose new obligations in areas such as privacy and liability for copyright infringement by third parties. The U.S. government, including the FTC and the Department of Commerce, has announced that it is reviewing the need for greater regulation for the collection of information concerning user behavior on the Internet, including regulation aimed at restricting certain online tracking and targeted advertising practices. Additionally, recent amendments to U.S. patent laws may affect the ability of companies, including us, to protect their innovations and defend against claims of patent infringement.

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

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

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

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

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

Our products and services involve the storage and transmission of users’ and advertisers’ information, and security breaches expose us to a risk of loss of this information, litigation and potential liability. We also work with third-party vendors to process credit card payments by our customers and are subject to payment card association operating rules. We experience cyber-attacks of varying degrees on a regular basis, and as a result, unauthorized parties have obtained, and may in the future obtain, access to our data or our users’ or advertisers’ data. For example, in February 2013, we disclosed that sophisticated unknown third parties had attacked our systems and may have had access to limited information for approximately 250,000 users. Any systems failure or compromise of our security that results in the unauthorized access to or release of our users’ or advertisers’ data, such as credit card data, could significantly limit the adoption of our products and services, as well as harm our reputation and brand and, therefore, our business. Our security measures may also be breached due to employee error, malfeasance or otherwise. Additionally, outside parties may attempt to fraudulently induce employees, users or advertisers to disclose sensitive information in order to gain access to our data or our users’ or advertisers’ data or accounts, or may otherwise obtain access to such data or accounts. Since our users and advertisers may use their Twitter accounts to establish and maintain online identities, unauthorized communications from Twitter accounts that have been compromised may damage their reputations and brands as well as ours. Because the techniques used to obtain unauthorized access, disable or degrade service or sabotage systems change frequently and often are not recognized until launched against a target, we may be unable to anticipate these techniques or to implement adequate preventative measures. If an actual or perceived breach of our security occurs, the market perception of the effectiveness of our security measures could be harmed, our users and advertisers may be harmed, lose trust and confidence in us, decrease the use of our products and services or stop using our products and services in their entirety. We may also incur significant legal and financial exposure, including legal claims, higher transaction fees and regulatory fines and penalties. Any of these actions could have a material and adverse effect on our business, reputation and operating results.

Our commerce efforts depend on third parties and are subject to evolving laws and regulations.

Since 2015, we have built commerce solutions that connect customers and retail partners. This includes enabling users to make purchases within a Tweet, load offers directly to a credit or debit card, and browse or shop collections of products without leaving Twitter.

We have relationships with third parties that perform a variety of functions such as credit card processing, tokenization, vaulting, currency conversion, fraud prevention and data security audits. If these third parties do not perform adequately or if our relationships with these third parties terminate, our retail partners’ ability to conduct business on Twitter could be adversely affected and our business and operating results could be adversely affected.

The laws and regulations related to e-commerce and payments are complex, subject to change, and vary across different jurisdictions in the United States and globally. As a result, we are required to spend significant time, effort and expense to comply with applicable laws and regulations. Any failure or claim of our failure to comply, or any failure or claim of failure by the above-mentioned third parties to comply, could increase our costs or could result in liabilities. Additionally, because Twitter accepts payment via credit cards and is certified as a PCI Level 1 service provider, we are subject to payment card association operating rules and certification requirements, including the Payment Card Industry Data Security Standard.

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

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

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

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

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

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

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

We also seek to obtain patent protection for some of our technology and as of December 31, 2015, we had 990 issued U.S. patents. We may be unable to obtain patent protection for our technologies, and our existing patents, and any patents that may be issued in the future, may not provide us with competitive advantages or distinguish our products and services from those of our competitors. In addition, any patents may be contested, circumvented, or found unenforceable or invalid, and we may not be able to prevent third parties from infringing or otherwise violating them. Effective protection of patent rights is expensive and difficult to maintain, both in terms of application and maintenance costs, as well as the costs of defending and enforcing those rights.

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

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

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

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

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

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

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

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

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

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

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

The number of our active users is calculated using internal company data that has not been independently verified. While these numbers are based on what we believe to be reasonable calculations for the applicable period of measurement, there are inherent challenges in measuring usage and user engagement across our large user base around the world. For example, there are a number of false or spam accounts in existence on our platform. We estimate that false or spam accounts represent less than 5% of our MAUs. However, this estimate is based on an internal review of a sample of accounts and we apply significant judgment in making this determination. As such, our estimation of false or spam accounts may not accurately represent the actual number of such accounts, and the actual number of false or spam accounts could be higher than we have currently estimated. We are continually seeking to improve our ability to estimate the total number of spam accounts and eliminate them from the calculation of our active users, but we otherwise treat multiple accounts held by a single person or organization as multiple users for purposes of calculating our active users because we permit people and organizations to have more than one account. Additionally, some accounts used by organizations are used by many people within the organization. As such, the calculations of our active users may not accurately reflect the actual number of people or organizations using our platform.

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

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

Our corporate culture has contributed to our success, and if we cannot maintain this culture as we grow, we could lose the innovation, creativity and teamwork fostered by our culture, and our business may be harmed.

We believe that our culture has been and will continue to be a key contributor to our success. From January 1, 2010 to December 31, 2015, we increased the size of our workforce by over 3,700 full-time employees, and we expect to continue to make investments in our employees. If we do not continue to develop our corporate culture or maintain our core values as we grow and evolve, we may be unable to foster the innovation, creativity and teamwork we believe we need to support our growth.

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

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

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

The number of people who access the Internet through devices other than personal computers, including mobile phones, tablets, video game consoles and television set-top devices, has increased dramatically in the past few years. In the three months ended December 31, 2015, over 85% of our advertising revenue was generated from mobile devices. Since we generate a majority of our advertising revenue through users on mobile devices, we must continue to drive adoption of our mobile applications. However, in emerging markets like India and Pakistan, most users use feature phones and communicate via SMS messaging, both of which have limited functionality and neither of which may be able to take full advantage of our products and services offered on smartphone or our website or desktop applications. In addition, mobile users frequently change or upgrade their mobile devices. Our business and operating results may be harmed if our users do not install our mobile application when they change or upgrade their mobile device. Although we generate the majority of our advertising revenue from ad engagements on mobile devices, certain of our products and services, including Promoted Trends and Promoted Accounts, receive less prominence on our mobile applications than they do on our desktop applications. This has in the past reduced, and may in the future continue to reduce, the amount of revenue we are able to generate from these products and services as users increasingly access our products and services through mobile and alternative devices. In addition, as new devices and platforms are continually being released, users may consume content in a manner that is more difficult to monetize. If we are unable to develop products and services that are compatible with new devices and platforms, or if we are unable to drive continued adoption of our mobile applications, our business and operating results may be harmed.

Future acquisitions and investments could disrupt our business and harm our financial condition and operating results.

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

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

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

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

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

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

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

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

In 2014, we issued $935.0 million principal amount of 0.25% convertible senior notes due 2019, or the 2019 Notes, and $954.0 million principal amount of 1.00% convertible senior notes due 2021, or the 2021 Notes and together with the 2019 Notes, the Notes, in private placements to qualified institutional buyers. As of December 31, 2015, we had a total par value of $1.89 billion of outstanding Notes.

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

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

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

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

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

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

Our income tax obligations are based in part on our corporate operating structure, including the manner in which we develop, value and use our intellectual property and the scope of our international operations. The tax laws applicable to our international business activities, including the laws of the United States and other jurisdictions, are subject to interpretation. The taxing authorities of the jurisdictions in which we operate may challenge our methodologies for valuing developed technology (or other intangible assets) or intercompany arrangements, which could increase our worldwide effective tax rate and harm our financial condition and operating results. We are subject to review and audit by U.S. federal and state and foreign tax authorities. Tax authorities may disagree with certain positions we have taken and any adverse outcome of such a review or audit could have a negative effect on our financial position and operating results. In addition, our future income taxes could be adversely affected by earnings being lower than anticipated in jurisdictions that have lower statutory tax rates and higher than anticipated in jurisdictions that have higher statutory tax rates, by changes in the valuation of our deferred tax assets and liabilities, or by changes in tax laws, regulations or accounting principles, as well as certain discrete items. Greater than anticipated tax expenses, or disputes with tax authorities, could adversely impact our operating results.

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

Under generally accepted accounting principles in the United States, or GAAP, we review our intangible assets for impairment when events or changes in circumstances indicate the carrying value may not be recoverable. Goodwill is required to be tested for impairment at least annually. As of December 31, 2015, we had recorded a total of $1.26 billion of goodwill and intangible assets. An adverse change in market conditions, particularly if such change has the effect of changing one of our critical assumptions or estimates, could result in a change to the estimation of fair value that could result in an impairment charge to our goodwill or intangible assets. Any such material charges may have a material negative impact on our operating results.

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

As of December 31, 2015, we had U.S. federal net operating loss carryforwards of approximately $3.37 billion and state net operating loss carryforwards of approximately $1.34 billion. Under Sections 382 and 383 of Internal Revenue Code of 1986, as amended, or the Code, if a corporation undergoes an “ownership change,” the corporation’s ability to use its pre-change net operating loss carryforwards and other pre-change tax attributes, such as research tax credits, to offset its post-change income and taxes may be limited. In general, an “ownership change” occurs if there is a cumulative change in our ownership by “5% shareholders” that exceeds 50 percentage points over a rolling three-year period. Similar rules may apply under state tax laws. In the event that it is determined that we have in the past experienced an ownership change, or if we experience one or more ownership changes as a result of future transactions in our stock, then we may be limited in our ability to use our net operating loss carryforwards and other tax assets to reduce taxes owed on the net taxable income that we earn. Any such limitations on the ability to use our net operating loss carryforwards and other tax assets could adversely impact our business, financial condition and operating results.

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

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

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

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

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

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

The market price of our common stock has been and may continue to be highly volatile in response to various factors, some of which are beyond our control. Since shares of our common stock were sold in our initial public offering in November 2013 at a price of $26.00 per share, the reported high and low sales prices of our common stock has ranged from $74.73 to $21.01, through December 31, 2015. 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. This litigation, if instituted against us, could result in substantial costs and a diversion of our management’s attention and resources.

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

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

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

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

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

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

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

As of December 31, 2015, we leased office facilities around the world totaling approximately 1,732,000 square feet, including 839,000 square feet for our corporate headquarters in San Francisco, California. We also lease data center facilities in the United States pursuant to various lease agreements and co-location arrangements with data center operators. We believe our facilities are sufficient for our current needs.

We are currently involved in, and may in the future be involved in, legal proceedings, claims and government investigations in the ordinary course of business. We are involved in litigation, and may in the future be involved in litigation, with third parties asserting, among other things, infringement of their intellectual property rights. In addition, the nature of our business exposes us to claims related to defamation, rights of publicity and privacy, and personal injury torts resulting from information that is published or made available on our platform. This risk is enhanced in certain jurisdictions outside the United States where our protection from liability for content published on our platform by third parties may be unclear and where we may be less protected under local laws than we are in the United States. Although the results of the legal proceedings, claims and government investigations in which we are involved cannot be predicted with certainty, we do not believe that there is a reasonable possibility that the final outcome of these matters will have a material adverse effect on our business, financial condition or operating results.

Future litigation may be necessary, among other things, to defend ourselves, our platform partners and our users 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.

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

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

As of February 17, 2016, there were 962 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.

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.

From January 1, 2015 through December 31, 2015, we issued an aggregate of 5,703,385 shares of our common stock in connection with our acquisitions of certain companies or their assets.

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

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

The following graph compares the cumulative total return to stockholders on our common stock relative to the cumulative total returns of the Standard & Poor’s 500 Index, or S&P 500, and the Dow Jones Internet Composite Index, or DJ Internet Composite. An investment of $100 (with reinvestment of all dividends) is assumed to have been made in our common stock and in each index on November 7, 2013, the date our common stock began trading on the NYSE, and its relative performance is tracked through December 31, 2015. The returns shown are based on historical results and are not intended to suggest future performance.

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

The consolidated statements of operations data for the years ended December 31, 2015, 2014 and 2013 and the consolidated balance sheet data as of December 31, 2015 and 2014 are derived from our audited consolidated financial statements included in Part II, Item 8, “Financial Statements and Supplementary Data” in this Annual Report on Form 10‑K. The consolidated statements of operations data for the year ended December 31, 2012 and 2011 and the consolidated balance sheet data as of December 31, 2013, 2012 and 2011 are derived from our audited consolidated financial statements not included in this Annual Report on Form 10-K. Our historical results are not necessarily indicative of the results that may be expected in the future.

	Year Ended December 31,
	2015			2014			2013			2012			2011
	(In thousands, except per share data)
Consolidated Statement of Operations Data:
Revenue	$	2,218,032		$	1,403,002		$	664,890		$	316,933		$	106,313
Costs and expenses⁽¹⁾
Cost of revenue		729,256			446,309			266,718			128,768			61,803
Research and development		806,648			691,543			593,992			119,004			80,176
Sales and marketing		871,491			614,110			316,216			86,551			25,988
General and administrative		260,673			189,906			123,795			59,693			65,757
Total costs and expenses		2,668,068			1,941,868			1,300,721			394,016			233,724
Loss from operations		(450,036	)		(538,866	)		(635,831	)		(77,083	)		(127,411	)
Interest expense		(98,178	)		(35,918	)		(7,576	)		(3,255	)		(1,271	)
Other income (expense), net		14,909			(3,567	)		(3,739	)		1,168			(1,064	)
Loss before income taxes		(533,305	)		(578,351	)		(647,146	)		(79,170	)		(129,746	)
Provision (benefit) for income taxes		(12,274	)		(531	)		(1,823	)		229			(1,444	)
Net loss	$	(521,031	)	$	(577,820	)	$	(645,323	)	$	(79,399	)	$	(128,302	)
Deemed dividend to investors in relation to the tender offer		—			—			—			—			35,816
Net loss attributable to common stockholders	$	(521,031	)	$	(577,820	)	$	(645,323	)	$	(79,399	)	$	(164,118	)
Net loss per share attributable to common stockholders:
Basic and diluted	$	(0.79	)	$	(0.96	)	$	(3.41	)	$	(0.68	)	$	(1.60	)
Weighted-average shares used to compute net loss per share attributable to common stockholders:
Basic and diluted		662,424			604,990			189,510			117,401			102,544
Other Financial Information:⁽²⁾
Adjusted EBITDA	$	557,807		$	300,896		$	75,430		$	21,164		$	(42,835	)
Non-GAAP net income (loss)	$	276,629		$	101,071		$	(34,330	)	$	(35,191	)	$	(65,533	)

	Year Ended December 31,
	2015		2014		2013		2012		2011
	(In thousands)
Cost of revenue	$	40,705	$	50,536	$	50,942	$	800	$	1,820
Research and development		401,537		360,726		379,913		12,622		33,559
Sales and marketing		156,904		157,263		114,440		1,346		1,553
General and administrative		82,972		63,072		55,072		10,973		23,452
Total stock-based compensation	$	682,118	$	631,597	$	600,367	$	25,741	$	60,384

	As of December 31,
	2015		2014		2013		2012			2011
	(In thousands)
Consolidated Balance Sheet Data:
Cash and cash equivalents	$	911,471	$	1,510,724	$	841,010	$	203,328		$	218,996
Short-term investments		2,583,877		2,111,154		1,393,044		221,528			330,543
Working capital		3,875,753		3,862,059		2,349,249		444,587			548,324
Property and equipment, net		735,299		557,019		332,662		185,574			61,983
Total assets		6,442,439		5,583,082		3,366,240		831,568			720,675
Convertible notes		1,455,095		1,376,020		—		—			—
Total liabilities		2,074,392		1,956,679		416,234		207,204			87,391
Redeemable convertible preferred stock		—		—		—		37,106			49
Convertible preferred stock		—		—		—		835,430			835,073
Total stockholders' equity (deficit)		4,368,047		3,626,403		2,950,006		(248,172	)		(201,838	)

To supplement our consolidated financial statements presented in accordance with generally accepted accounting principles in the United States, or GAAP, we consider certain financial measures that are not prepared in accordance with GAAP, including Adjusted EBITDA, non-GAAP net income (loss), revenue excluding foreign exchange effect and advertising revenue excluding foreign exchange effect. These non-GAAP financial measures are not based on any standardized methodology prescribed by GAAP and are not necessarily comparable to similarly-titled measures presented by other companies.

We define Adjusted EBITDA as net loss adjusted to exclude stock-based compensation expense, depreciation and amortization expense, interest and other expenses, provision (benefit) for income taxes and restructuring charges.

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

	Year Ended December 31,
	2015			2014			2013			2012			2011
	(In thousands)
Reconciliation of Net Loss to Adjusted EBITDA
Net loss	$	(521,031	)	$	(577,820	)	$	(645,323	)	$	(79,399	)	$	(128,302	)
Stock-based compensation expense		682,118			631,597			600,367			25,741			60,384
Depreciation and amortization expense		312,823			208,165			110,894			72,506			24,192
Interest and other expense, net		83,269			39,485			11,315			2,087			2,335
Provision (benefit) for income taxes		(12,274	)		(531	)		(1,823	)		229			(1,444	)
Restructuring charges		12,902			—			—			—			—
Adjusted EBITDA	$	557,807		$	300,896		$	75,430		$	21,164		$	(42,835	)

We define non-GAAP net income (loss) as net loss adjusted to exclude stock-based compensation expense, amortization of acquired intangible assets, non-cash interest expense related to our convertible notes, non-cash expense related to acquisitions, income tax effects related to acquisitions and restructuring charges.

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

	Year Ended December 31,
	2015			2014			2013			2012			2011
	(In thousands)
Reconciliation of Net Loss to Non-GAAP Net Income (Loss)
Net loss	$	(521,031	)	$	(577,820	)	$	(645,323	)	$	(79,399	)	$	(128,302	)
Stock-based compensation expense		682,118			631,597			600,367			25,741			60,384
Amortization of acquired intangible assets		54,659			36,563			16,530			18,687			4,697
Non-cash interest expense related to convertible notes		69,185			18,823			—			—			—
Non-cash expense related to acquisition		926			—			—			—			—
Income tax effects related to acquisitions		(22,130	)		(8,092	)		(5,904	)		(220	)		(2,312	)
Restructuring charges		12,902			—			—			—			—
Non-GAAP net income (loss)	$	276,629		$	101,071		$	(34,330	)	$	(35,191	)	$	(65,533	)

We use the non-GAAP financial measures of Adjusted EBITDA and non-GAAP net income (loss) in evaluating our operating results and for financial and operational decision-making purposes. We believe that Adjusted EBITDA and non-GAAP net income (loss) help identify underlying trends in our business that could otherwise be masked by the effect of the expenses that we exclude in Adjusted EBITDA and non-GAAP net income (loss). We believe that Adjusted EBITDA and non-GAAP net income (loss) provide useful information about our operating results, enhance the overall understanding of our past performance and future prospects and allow for greater transparency with respect to key metrics used by our management in its financial and operational decision-making.

These non-GAAP financial measures should not be considered in isolation from, or as a substitute for, financial information prepared in accordance with GAAP. There are a number of limitations related to the use of these non-GAAP financial measures rather than net loss, which is the nearest GAAP equivalent of these financial measures. Some of these limitations are:

We have attempted to compensate for these limitations by providing the nearest GAAP equivalents of these non-GAAP financial measures and describing these GAAP equivalents under the section titled “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Results of Operations.”

Item 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

The following discussion and analysis of our financial condition and results of operations should be read in conjunction with the consolidated financial statements and related notes thereto included in Item 8 “Financial Statements and Supplemental Data” in this Annual Report on Form 10-K. This discussion contains forward-looking statements that involve risks and uncertainties. Our actual results could differ materially from those discussed below. Factors that could cause or contribute to such differences include, but are not limited to, those identified below and those discussed in the section titled “Risk Factors” included elsewhere in this Annual Report on Form 10-K.

Net loss was $521.0 million and adjusted EBITDA was $557.8 million, resulting in an adjusted EBITDA margin of 25%, an increase of 21% compared to 2014.

Cash, cash equivalents and short-term investments in marketable securities totaled $3.50 billion as of December 31, 2015.

Total average monthly active users (MAUs) were 320 million for the three months ended December 31, 2015, up 9% compared to the three months ended December 31, 2014. Mobile MAUs represented approximately 80% of total MAUs.

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

Monthly Active Users (MAUs). We define MAUs as Twitter users who logged in or were otherwise authenticated and accessed Twitter through our website, mobile website, desktop or mobile applications, SMS or registered third-party applications or websites in the 30-day period ending on the date of measurement. Average MAUs for a period represent the average of the MAUs at the end of each month during the period. MAUs are a measure of the size of our logged in or otherwise authenticated active user base. In the three months ended December 31, 2015, we had 320 million average MAUs, which represents an increase of 9% from the three months ended December 31, 2014. The growth in average MAUs was driven primarily by growth initiatives. In the three months ended December 31, 2015, we had 65 million average MAUs in the United States and 254 million average MAUs in the rest of the world, which represent increases of 3% and 11%, respectively, from the three months ended December 31, 2014. For additional information on how we calculate MAUs and factors that can affect this metric, see the section titled “Note Regarding Key Metrics.”

In order to simplify our disclosures, we will no longer include SMS Fast Followers in our reported total MAUs going forward.

Changes in Ad Engagements and Cost Per Ad Engagement. We define an ad engagement as a user interaction with one of our pay-for-performance advertising products. Ad engagements with our advertising products are based on a user completing an objective set out by an advertiser such as expanding, retweeting, likes or replying to a Promoted Tweet, playing an embedded video, downloading or engaging with a promoted mobile application, clicking on a website link, signing up for marketing emails from advertisers, following the account that tweets a Promoted Tweet, or completing a transaction on an external website. We believe changes in ad engagements are one way to measure user engagement with our advertising products. We believe changes in cost per ad engagement are one way to measure demand.

In the three months ended December 31, 2015, ad engagements increased 153% from the three months ended December 31, 2014. The increase was driven by growth in video ad engagements, growth in ad engagements on third-party publishers’ websites, applications and other offerings, and stronger advertiser demand for our advertising products in the fourth quarter of 2015 compared to the fourth quarter of 2014. In the three months ended December 31, 2015, average cost per ad engagement decreased 41% from the three months ended December 31, 2014. The decrease in cost per ad engagement was primarily driven by a mix shift to auto-play video, partially offset by an increase in same-format prices for the majority of our advertising products.

User Growth and Monetization. User growth trends reflected in the number of MAUs and monetization trends reflected in advertising engagements are key factors that affect our revenue. As our user base and the level of engagement of our users grow, we believe the potential to increase our revenue grows.

User Growth. We have generally experienced significant growth in our number of users over the last several years. In general, a higher proportion of Internet users in the United States use Twitter than Internet users in other countries. Accordingly, in the future we expect our user growth rate in certain international markets, such as Argentina, Brazil, France, India, Japan and the Philippines, to continue to be higher than our user growth rate in the United States. However, we expect to face challenges in entering some markets, such as China, where access to Twitter is blocked, as well as certain other countries that have intermittently restricted access to Twitter. Restrictions or limitations on access to Twitter may adversely impact our ability to increase the size of our user base and generate additional revenue in certain markets.

We do not separately track whether an MAU has only used Twitter on a desktop or on a mobile device. However, in the three months ended December 31, 2015, approximately 80% of our average MAUs accessed Twitter from a mobile device, roughly stable from the three months ended December 31, 2014.

We may face challenges in increasing the size of our user base, including, among others, competition from alternative products and services, a decline in the number of influential users on Twitter or a perceived decline in the quality of content or user experience available on Twitter. We intend to drive growth in our user base by continuing to demonstrate the value and usefulness of our products and services to potential new users, by introducing new products, services and features and refining our core service. Our user growth rate has slowed over time, and we anticipate that it may continue to slow or decline. To the extent our logged-in user growth or user growth rate continues to slow or the absolute number of logged in users declines, our revenue growth will become increasingly dependent on our ability to increase levels of user engagement on Twitter and monetizing our total audience on logged-out usage and syndicated properties as well as increasing revenue growth from third party publishers’ websites, applications and other offerings.

Monetization. There are many variables that impact the monetization of our platform, such as the number of MAUs, our users’ level of engagement with our platform, ad load (which is a function of the amount of advertising we choose to display), our users’ engagement with our Promoted Products, advertiser demand and cost per ad engagement. Generally, we design our algorithms for our pay-for-performance Promoted Products on Twitter to optimize the overall user experience and the value we deliver to advertisers. We have, and may in the future, increase ad load to the extent that we are able to continue to reach the right balance of advertiser value and the overall user experience. In order to improve monetization, we plan to increase the value of our advertising services by continuing to increase the size and engagement of our user base as well as improve our ability to target advertising to our users’ interests and the ability of our advertisers to optimize their campaigns and measure the results of their campaigns.

Although the majority of the Promoted Products we sell to our advertisers are placed on Twitter, we have been growing our advertising revenue by selling to advertisers our advertising products that we place on third-party publishers’ websites, applications or other offerings. For the latter category of advertising placements, we incur additional costs, particularly traffic acquisition costs, to fulfill our services to advertisers. This mix shift of additional advertising revenue being generated from such third-party placements may continue in the future.

In the three months ended December 31, 2015, over 85% of our advertising revenue was generated from mobile devices. We have experienced strong growth in advertising revenue from mobile devices because user engagement is significantly higher on mobile applications than on our desktop applications, and we expect this trend to continue. However, Promoted Accounts and Promoted Trends receive less prominence on our mobile applications than they do on our desktop applications, which means that fewer users see them displayed on our mobile applications, resulting in fewer ad engagements with Promoted Accounts and fewer impressions of Promoted Trends on mobile applications. Primarily as a result of Promoted Accounts and Promoted Trends receiving less prominence on mobile applications, we have generated higher monetization of our ad engagements on our desktop applications than on our mobile applications. Although our cost per ad engagement on our desktop applications is higher than our cost per ad engagement on our mobile applications, the substantial majority of our ad engagements and advertising revenue is generated from mobile applications.

We intend to continue to increase the monetization of our platform by improving the targeting capabilities of our advertising services to enhance the value of our Promoted Products for advertisers, expanding our sales efforts to reach advertisers in additional international markets, opening our platform to additional advertisers through our self-serve advertising platform and developing new ad formats for advertisers.

Effectiveness of Our Advertising Services. Advertisers can use Twitter to communicate directly with their followers for free, but many choose to purchase our advertising services to reach a broader audience and further promote their brands, products and services. We believe that increasing the effectiveness of our Promoted Products for advertisers will increase the amount that advertisers spend with us. We aim to increase the value of our Promoted Products by increasing the size and engagement of our user base, improving our ability to target advertising to our users’ interests and improving the ability of our advertisers to optimize their campaigns and measure the results of their campaigns. We may also develop new advertising products and services.

International Expansion. We intend to invest in our international operations in order to expand our user base and advertiser base and increase user engagement and monetization internationally. In the three months ended December 31, 2015, we had 254 million average MAUs internationally compared to 65 million average MAUs in the United States. In addition, our number of users is growing at a faster rate in many international markets, such as Argentina, Brazil, France, India, Japan and the Philippines. However, we derive the majority of our advertising revenue from advertisers in the United States. In order to increase our international advertising revenue, we plan to invest in our international operations. In the near term, we plan to increase the size of our sales and marketing support teams in international markets such as Brazil, Ireland, Japan, Middle East and UK.

We face challenges in increasing our advertising revenue internationally, including local competition, differences in advertiser demand, differences in the digital advertising market and conventions, and differences in the manner in which Twitter is accessed and used internationally. We face competition from well-established competitors in certain international markets. In addition, certain international markets are not as familiar with digital advertising in general, or with new forms of digital advertising, such as our Promoted Products. In these jurisdictions we are investing to educate advertisers about the benefits of our advertising services. However, we expect that it may require a significant investment of time and resources to educate advertisers in many international markets. We also face challenges in providing certain advertising products, features or analytics in certain international markets, such as the European Union, due to government regulation. In addition, in certain emerging markets, many users access Twitter through feature phones with limited functionality, rather than through smartphones, our website or desktop applications. This limits our ability to deliver certain features to these users and may limit the ability of advertisers to deliver compelling ads to users in these markets. We are investing to improve our applications for feature phones in order to improve our ability to monetize our products and services in international markets.

Competition. We face significant competition for users and advertisers. We compete against many companies to attract and engage users and for advertiser spend, including companies with greater financial resources and substantially larger user bases which offer a variety of Internet and mobile device-based products, services and content. In recent years there has been a significant number of acquisitions and consolidation activity by and among our actual and potential competitors. We must compete effectively for users and advertisers in order to grow our business and increase our revenue. We believe that our ability to compete effectively for users depends upon a number of factors, including the quality of our products and services; and our ability to compete effectively for advertisers depends upon a number of factors, including our ability to offer attractive advertising products with unique targeting capabilities and the size of our active user base. We intend to continue to invest in research and development to improve our products and services for users and advertisers and to grow our active user base in order to address the competitive challenges in our industry. As part of our strategy to improve our products and services, we may acquire other companies to add engineering talent or complementary products and technologies.

Investment in Infrastructure. We intend to increase the capacity and enhance the capability and reliability of our infrastructure. Our infrastructure is critical to providing users, platform partners, advertisers and data partners access to our platform, particularly during major planned and unplanned events, such as elections, sporting events or natural disasters, when activity on our platform increases dramatically. As our user base and the activity on our platform grow, we expect that investments and expenses associated with our infrastructure will continue to grow. These investments and expenses include the expansion of our data center operations and related operating costs, additional servers and networking equipment to increase the capacity of our infrastructure and increased bandwidth costs.

Products and Services Innovation. Our ability to increase the size and engagement of our user base, attract advertisers and increase our revenue will depend, in part, on our ability to improve existing products and services and to successfully develop or acquire new products and services. We plan to continue to make significant investments in research and development and, from time to time, we may acquire companies to enhance our products, services and technical capabilities.

Investment in Talent. We intend to invest in hiring and retaining talented employees to grow our business and increase our revenue. As of December 31, 2015, we had 3,898 full-time employees, an increase of over 260 full-time employees, or approximately 7%, from December 31, 2014. We expect to increase headcount for the foreseeable future as we continue to invest in our business. We have also made, and intend to continue to make, acquisitions that add engineers, designers, product managers and other personnel with specific technology expertise. In addition, we must retain our high-performing personnel in order to continue to develop, sell and market our products and services and manage our business.

Seasonality. Advertising spending is traditionally strongest in the fourth quarter of each year. Historically, this seasonality in advertising spending has affected our quarterly results, with higher sequential advertising revenue growth from the third quarter to the fourth quarter compared to sequential advertising revenue growth from the fourth quarter to the subsequent first quarter. For example, our advertising revenue increased 43%, 35% and 25% between the third and fourth quarters of 2013, 2014 and 2015, respectively, while advertising revenue for the first quarter of 2014 and 2015 increased 3% and decreased 10% compared to the fourth quarter of 2013 and 2014, respectively. The rapid growth in our business may have partially masked seasonality to date and the seasonal impacts may be more pronounced in the future.

Stock-Based Compensation Expense. We have historically utilized, and intend to continue to utilize, various forms of stock-based awards in order to hire and retain talented employees. During the twelve months ended December 31, 2015 and 2014, we recognized $682.1 million and $631.6 million of expense related to stock-based compensation, respectively. As of December 31, 2015, we had unrecognized stock-based compensation expense of approximately $1.25 billion related to outstanding equity awards, after giving effect to estimated forfeitures, which we expect to recognize over a weighted-average period of approximately three years. The stock-based compensation expenses related to our outstanding equity awards have a significant impact on our ability to generate net income on a GAAP basis in future periods.

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

Title of each class		Name of each exchange on which registered
Common Stock, Par Value $0.000005 Per Share		New York Stock Exchange

Large accelerated filer	x		Accelerated filer	¨
Non-accelerated filer	¨	(Do not check if a smaller reporting company)	Smaller reporting company	¨

	PART I	Page

Item 1.	Business	5

Item 1A.	Risk Factors	10

Item 1B.	Unresolved Staff Comments	35

Item 2.	Properties	36

Item 3.	Legal Proceedings	36

Item 4.	Mine Safety Disclosures	36

	PART II

Item 5.	Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities	37

Item 6.	Selected Financial Data	38

Item 7.	Management’s Discussion and Analysis of Financial Condition and Results of Operations	42

Item 7A.	Quantitative and Qualitative Disclosures About Market Risk	61

Item 8.	Financial Statements and Supplementary Data	63

Item 9.	Changes in and Disagreements With Accountants on Accounting and Financial Disclosure	99

Item 9A.	Controls and Procedures	99

Item 9B.	Other Information	99

	PART III

Item 10.	Directors, Executive Officers and Corporate Governance	100

Item 11.	Executive Compensation	100

Item 12.	Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters	100

Item 13.	Certain Relationships and Related Transactions, and Director Independence	100

Item 14.	Principal Accounting Fees and Services	100

	PART IV

Item 15.	Exhibits, Financial Statement Schedules	101

	Signatures	102

	2015				2014
	High		Low		High		Low
First Quarter	$	51.87	$	35.54	$	70.43	$	43.31
Second Quarter		53.49		33.51		47.59		29.51
Third Quarter		38.82		21.01		53.64		35.95
Fourth Quarter		31.87		21.99		55.99		34.62