Duolingo, Inc. is an American educational technology company that produces learning apps and provides language certification. Duolingo offers courses on 42 languages,[5] ranging from English, French, and Spanish to less commonly studied languages such as Welsh, Irish, and Navajo, and even constructed languages such as Esperanto and Klingon.[6] It also offers courses on music,[7] math, and chess.[8] The learning method incorporates gamification to motivate users with points, rewards and interactive lessons featuring spaced repetition.[9] The app promotes short, daily lessons for consistent, phased practice.
Duolingo also offers the Duolingo English Test, an online language assessment, and Duolingo ABC, a literacy app designed for children. The company follows a freemium model, where some content is provided for free with advertising, and users can pay for ad-free services which provide additional features.
History
Early history
The idea of Duolingo was formulated in 2009 by Carnegie Mellon University professor Luis von Ahn and his Swiss-born post-graduate student Severin Hacker.[10][11] Von Ahn had sold his second company, reCAPTCHA, to Google and, with Hacker, wanted to work on an education-related project.[12] Von Ahn stated that he saw how expensive it was for people in his community in Guatemala to learn English. Hacker (co-founder and current CTO of Duolingo) believed that "free education will really change the world" and wanted to provide an accessible means for doing so. He was recognized by the National Inventors Hall of Fame for his contributions to language learning and technological development.[13] The Duo mascot is a green owl because co-founder Severin Hacker hates the color green.[14]
The project was originally financed by von Ahn's MacArthur fellowship and a National Science Foundation grant.[15][16][17] The founders considered creating Duolingo as a nonprofit organization, but von Ahn judged this model unsustainable. Its early revenue stream, a crowdsourced translation service, was replaced by a Duolingo English Test certification program, advertising, and subscription.[18]
Funds
In October 2011, Duolingo announced that it had raised $3.3 million from a Series A round of funding, led by Union Square Ventures, with participation from author Tim Ferriss and actor Ashton Kutcher's investing firm A-Grade Investments.[19] Duolingo launched a private beta on November 30, 2011, and accumulated a waiting list of more than 100,000 people by December 13.[20][21] It launched to the general public on June 19, 2012, at which point the waiting list had grown to around 500,000.[11][22]
In September 2012, Duolingo announced that it had raised a further $15 million from a Series B funding round led by New Enterprise Associates, with participation from Union Square Ventures.[23] In November 2012, Duolingo released an iPhone app,[24] followed by an Android app in May 2013, at which time Duolingo had around 3 million users.[25] By July 2013, it had grown to 5 million users and was rated the No. 1 free education app in the Google Play Store.[26]
In February 2014, Duolingo announced that it had raised $20 million from a Series C funding round led by Kleiner Caufield & Byers, with prior investors also participating.[27] At this time, it had 34 employees, and reported about 25 million registered users and 12.5 million active users;[27] it later reported a figure closer to 60 million users.
In June 2015, Duolingo announced that it had raised $45 million from a Series D funding round led by Google Capital, bringing its total funding to $83.3 million. The round valued the company at around $470 million, with 100 million registered users globally.[18][28] In April 2016, it was reported that Duolingo had more than 18 million monthly users.[29][30]
In July 2017, Duolingo announced that it had raised $25 million in a Series E funding round led by Drive Capital, bringing its total funding to $108.3 million. The round valued Duolingo at $700 million, and the company reported passing 200 million registered users, with 25 million active users.[31] It was reported that Duolingo had 95 employees.[32] Funds from the Series E round would be directed toward creating initiatives such as a related educational flashcard app, TinyCards, and testbeds for initiatives related to reading and listening comprehension.[33] On August 1, 2018, Duolingo surpassed 300 million registered users.[34]
In December 2019, it was announced that Duolingo raised $30 million in a Series F funding round from Alphabet's investment company, CapitalG.[35] The round valued Duolingo at $1.5 billion. Duolingo reported 30 million active users at this time. The headcount at the company had increased to around two hundred, and new offices had been opened in Seattle, New York, and Beijing.[36] Duolingo planned to use the funds to develop new products and further expand its team in sectors like engineering, business development, design, curriculum and content creators, community outreach, and marketing.[37]
Features and media
In October 2013, Duolingo launched a crowdsourced language incubator.[38] Initially relying on volunteers developing its courses, in March 2021 Duolingo announced that it would be ending its volunteer contributor program. The company said that language courses would instead be maintained and developed by professional linguists aligning with CEFR standards.[39][40][41] On June 28, 2021, Duolingo filed for an initial public offering on NASDAQ under the ticker DUOL.[42] From August 2021 to June 2022, the Duolingo language learning app was removed from some app stores in China.[43] In March 2022, Duolingo discontinued its community forums.[44][45]
In August 2022, Duolingo overhauled its interface, changing its course structure from a tree-like design, where users could choose from a range of lessons after completing previous ones, to a linear progression. This update has been criticized by users across social media outlets, such as Reddit and X (formerly Twitter).[46] CEO Luis von Ahn stated that there were no plans to reverse the changes.[47]
In October 2022, Duolingo acquired Detroit-based animation studio Gunner, a long-time design and animation partner that had produced graphics and animations for Duolingo, Duolingo ABC, and the company’s marketing campaigns.[48][49]
In March 2023, Duolingo officially announced the planned Duolingo Max, a subscription tier above Super Duolingo, in their blog.[50] In October 2023, Duolingo released math and music courses in English and Spanish for iOS users.[51][52]
In January 2024, Duolingo fired around ten percent of its contract workforce and announced plans to replace them with AI.[53][54] The company acquired Detroit-based design studio Hobbes in March.[55]
Duolingo announced plans to expand its music education offerings after acquiring London-based NextBeat, a music and gaming start-up company.[56]
Products and services
Courses
Language courses
CEFR based language courses for learners of English, Spanish, French, Italian, Chinese (Mandarin), Japanese, Korean, Portuguese, and German are available for all users.[57] Additional courses are also available for speakers of English (Arabic, Czech, Danish, Dutch, Esperanto, Finnish, Greek, Haitian Creole, Hawaiian, Hebrew, High Valyrian, Hindi, Hungarian, Indonesian, Irish, Klingon, Latin, Navajo, Norwegian, Polish, Romanian, Russian, Scottish Gaelic, Swahili, Swedish, Turkish, Ukrainian, Vietnamese, Welsh, Yiddish, Zulu), Chinese (Chinese (Cantonese)), Arabic (Swedish), and Spanish (Catalan, Guarani, Russian, Swedish).
Language courses
CEFR based language courses for learners of English, Spanish, French, Italian, Chinese (Mandarin), Japanese, Korean, Portuguese, and German are available for all users.[57] Additional courses are also available for speakers of English (Arabic, Czech, Danish, Dutch, Esperanto, Finnish, Greek, Haitian Creole, Hawaiian, Hebrew, High Valyrian, Hindi, Hungarian, Indonesian, Irish, Klingon, Latin, Navajo, Norwegian, Polish, Romanian, Russian, Scottish Gaelic, Swahili, Swedish, Turkish, Ukrainian, Vietnamese, Welsh, Yiddish, Zulu), Chinese (Chinese (Cantonese)), Arabic (Swedish), and Spanish (Catalan, Guarani, Russian, Swedish).
Subscriptions
Super Duolingo
As of 2014, most of Duolingo's language learning features are free with advertising. Users can remove advertising by paying a subscription fee or promoting referral links.[58] The paid user program, Super Duolingo (formerly known as Duolingo Plus), offers unlimited retries and access to some additional types of lessons. It is otherwise identical to Duolingo for Schools.[59][60][61][62]
Duolingo Max
Duolingo Max is a subscription above Super Duolingo that adds additional functions using generative AI: Roleplay, an AI conversation partner; and Video Call, where users can video chat with one of the characters, which currently includes only Lily. It is intended to provide immersion through conversation.[63]. Explain My Answer - a AI generated feature to help users understand their mistakes - used to be Max exclusive, but is now free for all users as of 2026. [64]
Duolingo for Schools
Duolingo for Schools is designed to help teachers use Duolingo in their classrooms. It allows teachers to create classrooms, assign lessons, track student progress, and personalize learning.[65]
Super Duolingo
As of 2014, most of Duolingo's language learning features are free with advertising. Users can remove advertising by paying a subscription fee or promoting referral links.[58] The paid user program, Super Duolingo (formerly known as Duolingo Plus), offers unlimited retries and access to some additional types of lessons. It is otherwise identical to Duolingo for Schools.[59][60][61][62]
Duolingo Max
Duolingo Max is a subscription above Super Duolingo that adds additional functions using generative AI: Roleplay, an AI conversation partner; and Video Call, where users can video chat with one of the characters, which currently includes only Lily. It is intended to provide immersion through conversation.[63]. Explain My Answer - a AI generated feature to help users understand their mistakes - used to be Max exclusive, but is now free for all users as of 2026. [64]
Duolingo for Schools
Duolingo for Schools is designed to help teachers use Duolingo in their classrooms. It allows teachers to create classrooms, assign lessons, track student progress, and personalize learning.[65]
Duolingo English Test
The Duolingo English Test (DET) is an online English proficiency test that measures proficiency in reading, writing, speaking, and listening in English. It is a computer-based test scored on a scale of 10–160, with scores above 120 considered English proficiency. The test's questions algorithmically adjust to the test-takers' ability level.
Other programs
Duolingo Math was an app course for learning elementary mathematics. It was announced on YouTube on August 27, 2022.[66] It was merged into Duolingo in 2024, now available as a course.
On October 11, 2023, the company released Duolingo Music,[52] a new platform within the existing app that provides basic music learning through piano and sheet music lessons.[67][68]
Duolingo introduced chess lessons in beta on April 22, 2025,[69] with an initial rollout planned for iOS in English by May. The lessons are structured around the Elo rating system, gradually increasing in difficulty to match the user's skill level. Learners can play mini-matches or full games against Duolingo's virtual chess coach, Oscar, whose difficulty also scales with progress. At launch, users are not able to play against each other.[70][71]
Duolingo ABC is a free app designed for young children to learn letters, their sounds, phonics, and other early reading concepts. Released in 2020, it does not contain ads or in-app purchases. As of April 2024, iOS and Android versions are available, but only in English.[8][72]
Learning model
Exercises and pacing
On Duolingo, learners learn by doing, engaging with the course material.[73] Lessons are designed to be brief, allowing users to learn in manageable chunks.[74][75] Duolingo uses a gamified approach to learning, with lessons that incorporate translating, interactive exercises, quizzes, and stories.[76] It also uses an algorithm that adapts to each learner and can provide personalized feedback and recommendations.
Gamification
Duolingo provides a competitive space,[77] such as in leagues, where people can compete with randomly selected groupings of up to 30 users. Leagues: Bronze, Silver, Gold, Sapphire, Ruby, Emerald, Amethyst, Pearl, Obsidian, Diamond. Rankings in leagues are determined by the number of experience points earned in a week. Badges in Duolingo represent achievements earned from completing specific objectives.[78] Users can also create their own avatars.[79][80]
Any lesson completed in Duolingo will count towards the user's daily streak.[52] The daily streak 's visual symbol in the app is fire. Duolingo's "Friend Streak" lets users maintain streaks with up to five friends.[81] Streaks encourage consistent daily practice and help build a habit of regular learning.
The app has a personalized bandit algorithm system (later the A/B tested variant recovering difference softmax algorithm) that determines the daily notification that will be sent out to the user.[82]
Duolingo Score
The Duolingo Score is an estimate of users' proficiency in the language they're learning in CEFR-aligned courses. Duolingo Score provides a granular assessment of what a student has learned and what they can do with the language.[83] DET is using a similar scoring system. The most developed CEFR-aligned courses (French, English and Spanish) cover Duolingo Score from 0 to 130.
Business model
Duolingo operates on a freemium business model, offering free access to its learning platforms with ads. Revenue is primarily generated through subscriptions, which remove ads, and provide other perks like unlimited energy (formerly hearts) and generative AI. The app also generates income from in-app purchases of virtual currency (Gems) and power-ups that enhance the learning experience. Another key revenue stream is the Duolingo English Test (DET), a low-cost English proficiency test.[84]
In April 2020, it passed one million paid subscribers;[85] it reached 2.9 million in March 2022,[86] and 4.8 million at the end of March 2023.[87] As of June 2025, Duolingo has 10.9 million paying subscribers.[88]
Duolingo had revenue of $531 million in 2023, compared to $250.77 million in 2021,[89] $36 million in 2018,[90] $13 million in 2017,[34] and $1 million in 2016. In May 2022, it was reported that 6.8% of its monthly active users paid for the ad-free version of the app.[91]
Generative AI usage
Starting from 2024, Duolingo began to cut some of their staff following steps to incorporate AI into its platform.[92] By 2025, Duolingo planned to introduce 150 courses created using generative AI. Most of the courses created using AI were aimed at non-English speakers, such as the introduction of courses in several East Asian languages such as Japanese and Korean for Spanish speakers.[93] This move caused controversy with language researchers stating that the use of AI-generated content could take work away from future translators, as the courses would lose nuance in social-cultural aspects of certain languages that AI models cannot understand.[94]
In addition, company executives were questioned about statements indicating that the use of AI is much more effective than human teaching. These comments were removed from much of Duolingo's social media following backlash from users as well as professional translators.[95]
In 2025, CEO Luis von Ahn announced Duolingo would become an "AI-first" company and would be replacing contracted workers with artificial intelligence through automation.[96] This decision was met with public outcry, leading many users to unsubscribe and end their learning streaks in protest.[97] Many criticized the Duolingo app for losing its quality due to this change.[98]
In May 2025, due to backlash against the perceived threat of workers being replaced by inferior-quality AI, Duolingo's Instagram and TikTok videos were flooded with comments expressing anger at the company. Duolingo took down all videos from both channels. Duolingo's social media accounts had previously been described as models of success in marketing. The company later uploaded a video which sarcastically attempted to downplay the controversy, followed by a video from the CEO attempting to clarify the company's use of generative AI technology.[99][100][101] When asked about the backlash during Duolingo's August 2025 earnings call, CEO Luis von Ahn said: "We just don't believe that the effect of this is very material in terms of when you're looking at actual financial metrics."[102]
Reception
Effectiveness
A 2017 study found no significant difference between elementary students learning Spanish through the "gamification" of the Duolingo app and those learning in classroom environments, with both groups demonstrating a similar increase in achievements and self-efficacy.[103]
Duolingo's occasional use of 'erratic' phrases—such as "The bride is a woman and the groom is a hedgehog" or "The man eats ice cream with mustard"[104]—is reportedly derived from research published in 2018 by psychologists at Ghent University in Belgium,[105] which concluded that such "semantically unpredictable sentences" were more effective for language learning than conventional and predictable phrases, based on the concept of "reward prediction errors", in which unexpected or surprising outcomes are more rewarding and thus encourage further learning.[106][104]
A 2022 study on adults using Duolingo as their only language learning tool, published in the journal Foreign Language Annals, found that participants who completed a course had similar reading and listening proficiency to university students after four semesters of study, concluding that Duolingo could be an effective tool for language learning.[107] Another 2022 study of Malaysian students learning French, published by the National University of Malaysia Press, found that the app facilitated the acquisition of vocabulary and concluded that it was "well suited" for beginners in this regard.[108]
According to Duolingo's own 2021 study, five sections of the app are roughly equivalent to five semesters of university instruction, and Duolingo is an "effective tool [...] at an intermediate level".[109][110] A 2023 study funded by Duolingo concluded that Duolingo English learners did not significantly learn much grammar.[111] Duolingo English learners in Colombia and Spain were found to gain significantly more proficiency than students in a classroom, except for listening.[112]
Criticism
Some language professionals have criticized the app for its limitations and gamified design.[113] Users have also reported that "gamification" has led to cheating, hacking, and incentivized game strategies that conflict with actual learning.[114]
In January 2023, Duolingo's data on over 2.6 million users' usernames, names, and phone numbers was sold in a hacker forum. Duolingo later stated that they would investigate the "dark web post".[115] They concluded that the data was obtained by scraping publicly available information based on an exposed application programming interface (API).[116][117] Duolingo's spokesperson states that the API is intentionally publicly visible.
Since the end of October 2023, Duolingo has stopped updating its Welsh course to "focus on languages in higher demand". Some users criticized this decision because it came at the expense of learners of a language with limited resources on the market and the potential halting of the Welsh Government "Cymraeg 2050" strategy to promote Welsh language learning.[118][119]
Bruno Estigarribia stated that, as of 2019, the Guarani course was "seemingly in a development phase" and that it "had many inconsistencies". He added this course could serve as a complement to one's studies, but it would not "magically teach" the language.[120]
In January 2024, Duolingo fired about 10% of contractors, stating that "Generative AI is accelerating our work by helping us create new content dramatically faster."[121][122]
In April 2025, Duolingo announced they would gradually stop using contractors where "AI" can do the work, urging employees to "take occasional small hits on quality [rather] than move slowly and miss the moment" in order to become an "AI-first" company.[123] This statement was received poorly, and a follow-up post, where the CEO claims he was misunderstood, led to further critique.[124]
Awards
In 2013, Apple named Duolingo as its "iPhone App of the Year".[125] Duolingo won "Best Education Startup" at the 2014 Crunchies,[126][127] and was the most downloaded education app in Google Play in 2013 and 2014.[128]
In 2015, the Duolingo company won the Index Award in the Play & Learning category.[129]
Image and brand
Duolingo's characters
Duolingo has brand characters that are used for engagement and creating storylines.[130][131] The main characters include[132] Duo Keyshauna Renee Lingo, commonly known as Duo or Duo the Owl, the company's green owl mascot. On February 11, 2025, Duolingo announced, as part of a publicity stunt, that Duo had died,[133][134][135] after being hit by a Tesla Cybertruck.[136][137][138] Later, Duolingo put up a website where the users of the app would have to work together to obtain 50 Billion in-app experience to resurrect Duo.[139] After the goal was reached, Duolingo then posted a video on their social medias of Duo's resurrection.[140] The company also stated the character's birth date as 1000BC, and his full name as Duo Keyshauna Renee Lingo.[141][142] Duo served as the motivational face of the app, encouraging users to complete their lessons and maintain their learning streaks. Duo has become a well-known internet character, often depicted humorously as aggressively reminding users to not miss their streaks. Over time, Duo has gained a significant reputation in memes for being persistent—even threatening—about keeping users on track with their lessons. According to Duolingo Brand Guidelines, "Duo is a boy" and communicates through text only.[143]
In popular culture
Due to the app's frequent reminder notifications, Duolingo's mascot, a green cartoon owl named Duo, has been the subject of Internet memes antagonizing him, with the character often depicted stalking or threatening users if they do not continue using the app.[144][145]
Duolingo has leaned into its online reputation and has adjusted its social media and marketing strategies accordingly.[146] Acknowledging the meme, Duolingo released a video on April Fools' Day 2019, depicting a facetious new feature called "Duolingo Push". In the video, users of "Duolingo Push" are reminded to use the app by Duo himself (depicted by a person wearing a Duolingo mascot costume), who stares at and follows them until they comply.[147][148] It was also acknowledged during Duolingo's 2022 April Fools' Day video, "Lawyer Fights Duolingo Owl for $2,700,000", where a fictitious law firm fights for those that have been harmed by Duolingo's owl mascot.[149] This was further referenced by the company in its 2024 April Fools' Day skit "Duo on Ice", in which the owl, in a mix of Spanish and English, admitted to having an appetite for human flesh, and if the user failed to continue their streak, they would "eat their head like a praying mantis."[150]
In November 2019, Saturday Night Live parodied Duolingo in a sketch where adults learned to communicate with children by using a fictitious course called "Duolingo for Talking to Children".[151]
Offices and workforce
Duolingo is headquartered in Pittsburgh, Pennsylvania. Duo's Taqueria is an adjacent taco stand operated by Duolingo. The restaurant encourages patrons to order in Spanish. Duolingo's taco shop brought in $700,000 in 2023.[152]
In 2024, Duolingo opened a new office in New York City.[153][154]
Duolingo also has offices in Seattle, Detroit,[55] Beijing, and Berlin.[155]
As of October 2024, Duolingo employs around 850 people.[156]
See also
- Distance education
- Language assessment
- Language education
- Language pedagogy
- Mathematics education
- Music education
External links
References
- Duolingo, Inc. 2024 Annual Report (Form 10-K) U.S. Securities and Exchange Commission, 2025-02-28, retrieved March 2, 2025^
- Migrating Duolingo's Android app to 100% Kotlin blog.duolingo.com, 2020-04-06, retrieved September 17, 2020^
- Real World Swift – Making Duolingo Blog making.duolingo.com, 2015-01-07, retrieved October 22, 2018^
- Rewriting Duolingo's engine in Scala – Making Duolingo Blog making.duolingo.com, 2017-01-31, retrieved February 1, 2017^
- Matt. The Complete List Of EVERY Duolingo Language Duoplanet, February 20, 2023, retrieved 2022-09-21^
- Noah Higgins-Dunn. If you are a 'Game of Thrones' fan, this app will teach you how to speak in High Valyrian CNBC, 2019-04-14, retrieved 2022-05-23^
- Sabrina Ortiz. Duolingo opens waitlist for its new, free music course. Here's how to sign up ZDNET, retrieved 2023-10-11^
- Duolingo Team. Duolingo Math makes learning easy as pi(e) Duolingo, 2022-10-26, retrieved October 27, 2022^
- Dear Duolingo: Why is spaced repetition so important for learning? Duolingo Blog, 2023-12-26, retrieved 2024-08-02^
- M.G. Siegler. Meet Duolingo, Google's Next Acquisition Target; Learn A Language, Help The Web TechCrunch, 2011-04-12, retrieved 2014-11-21^
- Steven Loeb. When Duolingo was young: the early years VatorNews, 2018-06-22, retrieved 2019-12-21^
- Luis von Ahn. Luis Von Ahn's answer to What made Luis Von Ahn start Duolingo? retrieved 2021-05-14^
- Duolingo creator to be inducted into Inventors Hall of Fame NBC News, October 27, 2023, retrieved 2023-11-02^
- Dami Lee. Duolingo redesigned its owl to guilt-trip you even harder The Verge, 2018-12-13, retrieved 2024-06-06^
- Luis von Ahn. Online Education as a Vehicle for Human Computation U.S. National Science Foundation, 2017, retrieved April 6, 2018^
- Heather Masson-Forsythe. NSF gave Duolingo its wings! U.S. National Science Foundation, December 22, 2022, retrieved 25 March 2023^
- Jim Giles. Learn a language, translate the web New Scientist, January 11, 2012, retrieved August 26, 2017^
- Frederic Lardinois. Duolingo Raises $45 Million Series D Round Led By Google Capital, Now Valued At $470M TechCrunch, 2015-06-10, retrieved 2019-12-14^
- The Daily Start-Up: Kutcher-Backed Language Site Duolingo Finds Its Voice The Wall Street Journal, 2012-06-19, retrieved 2012-07-13^
- Adi Robertson. Duolingo will translate the internet while teaching languages The Verge, 2011-12-16, retrieved 2016-02-03^
- Ariel Schwartz. How The Creator of CAPTCHA Will Translate The Entire Internet Fast Company, 2011-12-13, retrieved 2025-02-09^
- Spice. Press Release: Duolingo.com Users Will Translate Web As They Learn a New Language Carnegie Mellon University, retrieved 2021-05-14^
- Duolingo Raises $15M Series B Round Led By NEA, Will Expand To More Languages And To Mobile Soon TechCrunch, 2012-09-17, retrieved 2019-12-13^
- Frederic Lardinois. Language Learning Service Duolingo Launches Its First iPhone App TechCrunch, AOL, 2012-11-13, retrieved 2016-04-18^
- Free Language Learning Service Duolingo Comes To Android TechCrunch, 2013-05-29, retrieved 2021-05-14^
- Dan Farber. Duolingo brings free language courses to the iPad C net, 2013-07-11, retrieved 2014-02-21^
- Duolingo Raises $20M Series C Led By Kleiner Perkins To Dominate Online Language Learning TechCrunch, 2014-02-14, retrieved 2021-05-14^
- 100M users strong, Duolingo raises $45M led by Google at a $470M valuation to grow language-learning platform VentureBeat, 2015-06-10, retrieved 2019-12-14^
- Duolingo Case Study – DynamoDB Amazon Web Services, Inc., 2016, retrieved 2019-12-23^
- . Duolingo Stores 31 Billion Items on Amazon DynamoDB and Uses AWS to Deliver Language Lessons April 25, 2016, retrieved 2019-12-23^
- Duolingo raises $25M at a $700M valuation TechCrunch, 2017-07-25, retrieved 2019-12-14^
- Duolingo. Duolingo Now Valued at $1.5 Billion www.prnewswire.com, retrieved 2019-12-14^
- Ramirez Elaine. Duolingo Is Launching A Korean Course To Cash In On Asia's Booming Language Market Forbes, retrieved 2017-10-11^
- Frederic Lardinois. Duolingo hires its first chief marketing officer as active user numbers stagnate but revenue grows TechCrunch, August 2018, retrieved 2019-12-14^
- Arun Janardhan. Duolingo's Luis von Ahn believes in the power of language Mintlounge, 2022-05-27, retrieved 2022-05-28^
- Paul Sawers. Duolingo raises $30 million from Alphabet's CapitalG at $1.5 billion valuation VentureBeat, 2019-12-04, retrieved 2019-12-13^
- Natasha Lindstrom. Duolingo touts $1.5B valuation; language company to hire 100 more people, mostly in Pittsburgh triblive.com, 2019-12-04, retrieved 2019-12-15^
- Juan Andres Munoz. Duolingo 'incubator' aims to crowdsource language teaching CNN, 2013-10-15, retrieved 2022-04-18^
- Ending & honoring our volunteer Contributor program Duolingo Blog, 2021-03-10, retrieved 2022-04-07^
- Emily Price. Language learning app Duolingo to mothball Welsh course Nation.Cymru, 2023-10-22, retrieved 2026-04-09^
- Shanti Mathias. When you can’t learn a language from your ancestors, learn from an app The Spinoff, 2022-02-03, retrieved 2026-04-09^
- Levi Sumagaysay. Duolingo, the fast-growing language-learning app, files for IPO MarketWatch, retrieved 2021-07-05^
- Duolingo back in China app stores after 1 year TechCrunch, 2022-06-10, retrieved 2022-07-26^
- Forum Announcement + FAQ Duolingo, retrieved June 6, 2024^
- Simone De Rochefort. Duolingo users are in turmoil over the app’s AI lessons Polygon.com, 2025-06-04, retrieved 2026-04-09^
- Bill Gifford. Can Duolingo Actually Teach You Spanish? Bloomberg Businessweek, 2022-12-02, retrieved 2022-12-02^
- Ben Goggin. Duolingo's redesign has some fans up in arms. Its CEO says it's not turning back. NBC News, 2022-08-26, retrieved 2022-08-26^
- Duolingo makes its first official acquisition, with more to come TechCrunch, October 4, 2022, retrieved 20 March 2026^
- Duolingo Acquires Gunner to Accelerate Product & Brand Development Duolingo Investor Relations, October 4, 2022, retrieved 20 March 2026^
- Introducing Duolingo Max, a learning experience powered by GPT-4 Duolingo Blog, 2023-03-14, retrieved 2024-04-24^
- Jamie Lang. Duolingo Acquires Detroit-Based Design And Animation Studio Gunner Cartoon Brew, 5 October 2022, retrieved 16 July 2023^
- One app to school them all: the expanded Duolingo 🎶 ➗ 🇲🇽 Duolingo Blog, 2023-10-11, retrieved 2023-10-11^
- Jennifer Korn. Duolingo lays off staff as language learning app shifts toward AI CNN, January 9, 2024, retrieved January 11, 2024^
- Beatrice Nolan. Duolingo lays off workers as it leans on AI tools to carry out more tasks Business Insider, January 10, 2024, retrieved January 11, 2024^
- Sarah Perez. Duolingo acquires Detroit-based design studio Hobbes TechCrunch, 2024-07-09, retrieved 2024-07-14^
- Michelle Caffrey. Duolingo to Expand in Music Education After U.K. Acquisition; German Ed-Tech Startup Raises €1M in Pre-Seed Round Marketbrief, 2025-08-14, retrieved 2025-10-01^
- Unofficial Duolingo Course Data duolingodata.com, retrieved 2025-01-23^
- Parmy Olson. Crowdsourcing Capitalists: How Duolingo's Founders Offered Free Education To Millions Forbes, January 22, 2014, retrieved 2015-12-22^
- What is Super Duolingo? Duolingo Help Center, retrieved 16 July 2023^
- Super Duolingo Super Duolingo homepage, retrieved 22 November 2024^
- The 'Miracle' of Duolingo: How Did It Become One of the Few Super-Growth Internet Companies in Recent Years? - Longbridge The 'Miracle' of Duolingo: How Did It Become One of the Few Super-Growth Internet Companies in Recent Years? - Longbridge, retrieved 2026-01-10^
- How Much Is Super Duolingo and How to Get It Cheaper with FamilyPro Breaking AC, retrieved 2026-01-10^
- Edwin Bodge, Bill Peterson. OpenAI customer story: Duolingo OpenAI, March 14, 2023, retrieved April 24, 2024^
- Duolingo. This Duolingo Feature Is Now Free 2026-01-01, retrieved 2026-02-16^
- Duolingo for Schools schools.duolingo.com, retrieved 2024-09-08^
- Sammi Siegel. Duolingo's Path to Math! • Sammi Siegel • Duocon 2022 Duolingo, August 27, 2022^
- Sarah Perez. Duolingo confirms its app will soon include both math and music lessons TechCrunch, 2023-09-06, retrieved 2023-10-06^
- Duolingo's new Music platform will teach you the basics of playing tunes TechRadar, 2023-10-11, retrieved 2023-10-11^
- Greta Cross. Duolingo adds chess to educational offers. Here's what to know about new, free course USA TODAY, retrieved 2025-07-01^
- GEEK STAFF. Duolingo adds chess lessons to iPhone app: here's what to expect Absolute Geeks, 2025-04-15, retrieved 2025-04-16^
- Ryan Deto. Duolingo expands app with chess launch Axios, 2025-04-22, retrieved 2025-04-22^
- Duolingo ABC: Unlocking the magic of reading Duolingo Blog, 2020-08-26, retrieved 2022-05-31^
- Duolingo. Introducing The Duolingo Method - How does Duolingo teach new subjects? 2023-10-11, retrieved 2024-08-02^
- Bozena Pajak, Karin Tsai. How we've improved the Duolingo learning experience this year (and a sneak peek toward 2020!) Duolingo Blog, 2019-12-11, retrieved 2021-08-26^
- Duolingo TESL-EJ, retrieved December 31, 2021^
- Dayna Brockbank. Everything You Need to Know About Duolingo Stories • Happily Ever Travels Happily Ever Travels, 2020-10-05, retrieved 2021-08-26^
- Guilherme Fians. Esperanto Revolutionaries and Geeks: Language Politics, Digital Media and the Making of an International Community Palgrave Macmillan, 2021, retrieved December 2, 2022^
- Duy Huynh, Long Zuo, Hiroyuki Iida. Games and Learning Alliance Springer, Cham, 2016^
- Duolingo Path. Duolingo Clash 2024-09-07, retrieved 2024-09-08^
- Become a Duolingo character with our new Avatars! Duolingo Blog, 2023-07-19, retrieved 2024-09-08^
- Friend Streak: a new way to stay motivated together Duolingo Blog, 2024-08-05, retrieved 2024-09-08^
- Kevin P. Yancey, Burr Settles. Proceedings of the 26th ACM SIGKDD International Conference on Knowledge Discovery & Data Mining Association for Computing Machinery, August 20, 2020^
- Kevin Yang. The Duolingo Score Tracks Your Learning Progress Duolingo Blog, 2024-10-23, retrieved 2025-01-28^
- Duolingo shareholder letter 2022 retrieved May 28, 2022^
- Nate Doughty. Duolingo passes one million paid users, expands with new hires Pittsburgh Business Times, 2020-04-08, retrieved 2020-12-12^
- Duolingo Announces Record Bookings in First Quarter 2022 and Raises Full Year Guidance retrieved May 25, 2022^
- Duolingo Reports 62% DAU Growth, 42% Revenue Growth, and Increased Profitability in First Quarter 2023; Raises Full Year Guidance retrieved May 31, 2023^
- Duolingo quarterly paid subscribers 2025 Statista, retrieved 2025-08-13^
- Ouyang Shijia. Language-learning app Duolingo bullish on Chinese market China Daily, 13 December 2019, retrieved 2019-12-14^
- Susan Adams. Game of Tongues: How Duolingo Built A $700 Million Business With Its Addictive Language-Learning App Forbes, retrieved 2019-12-14^
- Duolingo CEO talks earnings, paid subscribers, and the stock's performance Yahoo! Finance, May 19, 2022, retrieved 8 August 2024^
- Duolingo cuts workers as it relies more on AI The Washington Post, 2024-01-10, retrieved 2025-07-17^
- Amid Backlash, Duolingo Backtracks on Plans for AI Pivot PCMAG, 2025-05-25, retrieved 2025-07-17^
- Greg Toppo. As Duolingo Turns to AI, Some Users Say Language App Has Joined 'The Dark Side' The 74, 2025-06-03, retrieved 2025-07-17^
- Natalie Stechyson. Duolingo's CEO says AI will soon replace teachers. But... should it CBC News, 2025-05-22, retrieved 2025-07-17^
- Jonathan Limehouse. Duolingo going 'AI-first', replacing contractors with artificial intelligence: CEO USA TODAY, retrieved 2025-05-07^
- Duolingo Flooded by Pledges to Quit the App Following Decision to Replace Contractors With AI: 'That Owl is Dead to Me' www.msn.com, retrieved 2025-05-07^
- Duolingo deletes all TikTok videos and sends CEO bizarre message after "AI-first" backlash Cybernews, 2025-05-21, retrieved 2025-06-23^
- Reece Rogers. The AI Backlash Keeps Growing Stronger Wired, 20 June 2025, retrieved 4 August 2025^
- Joe Berkowitz. Duolingo deletes all its TikTok videos after AI backlash—and then returns with a strange message Fast Company, 20 May 2025, retrieved 4 August 2025^
- Victor Tangermann. Duolingo CEO Expresses Astonishment That People Were Mad When He Bragged About Replacing Workers With AI Futurism, 9 June 2025, retrieved 4 August 2025^
- Ryan Vlastelica. Duolingo Faces AI Risks as Investors Reconsider Its Pricey Multiple -… Bloomberg News, 2025-09-16, retrieved 2025-09-17^
- Jason R. Rachels, Amanda J. Rockinson-Szapkiw. The effects of a mobile gamification app on elementary students' Spanish achievement and self-efficacy Computer Assisted Language Learning, Routledge, 2018^
- Jane C. Hu. Why Are Duolingo's Sentences So Weird? Slate, 2021-11-29, retrieved 2024-07-26^
- Esther De Loof, Kate Ergo, Lien Naert, Clio Janssens, Durk Talsma, Filip Van Opstal, Tom Verguts. Signed reward prediction errors drive declarative learning PLOS ONE, 2018-01-02^
- Christian Benoît, Martine Grice, Valérie Hazan. The SUS test: A method for the assessment of text-to-speech synthesis intelligibility using Semantically Unpredictable Sentences Speech Communication, 1996^
- Xiangying Jiang, Joseph Rollinson, Luke Plonsky, Erin Gustafson, Bozena Pajak. Evaluating the reading and listening outcomes of beginning-level Duolingo courses Foreign Language Annals, 2022-01-11^
- Suziana Mat Saad, Nur Ameera Abd Rahim. Vocabulary Acquisition Using Duolingo in French Language Learning: A Malaysian Context E-Bangi: Journal of Social Sciences & Humanities, 2022^
- Duolingo Really Works - Learn more about how Duolingo works for learners Duolingo, retrieved 2024-06-06^
- Xiangying Jiang, Haoyu Chen, Lucy Portnof, Erin Gustafson, Joseph Rollinson, Luke Plonsky, Bozena Pajak. Finishing half of B1 on Duolingo comparable to five university semesters in reading and listening Duolingo, November 11, 2021^
- Rodrigo A. Rodríguez-Fuentes, Aleksandra Swatek. A Comparison Between Classroom and MALL Instruction with Duolingo: Learning English at the A2 CEFR Level Amazon Web Services, December 14, 2023, retrieved May 9, 2024^
- Beatriz González-Fernández. The effectiveness of Duolingo vs. classroom instruction on Spanish speakers' L2 English proficiency and lexical development Amazon Web Services, November 30, 2023^
- Katie Heaney. Is It Just Me, or Does Duolingo Not Work? The Cut, January 25, 2019, retrieved 24 November 2023^
- Robert Guthrie. Duolingo Is An App For Language-Learning, So Why Is It Plagued With Cheaters? Kotaku, 5 June 2023, retrieved 6 June 2023^
- Jonathan Greig. DuoLingo investigating dark web post offering data from 2.6 million accounts The Record, January 24, 2023, retrieved 2024-06-06^
- Alessandro Mascellino. Data of 2.6M Duolingo Users Leaked on Hacking Forum Infosecurity Magazine, 2023-08-24, retrieved 2024-06-06^
- Ernestas Naprys. Hackers exposed 2.6 million Duolingo users, more available for scraping Cybernews, November 15, 2023, retrieved June 6, 2024^
- James McCarthy, Owain Evans. Welsh course to be 'paused' on language app Duolingo October 24, 2023, retrieved 27 March 2024^
- Catriona Aitken. Duolingo: Language app boss to help Welsh language goal BBC News, 2023-10-30, retrieved 2024-06-07^
- Bruno Estigarribia. A Grammar of Paraguayan Guarani UCL Press, 2020^
- Jennifer Korn. Duolingo lays off staff as language learning app shifts toward AI January 9, 2024, retrieved 2025-10-02^
- Luis von Ahn. shareholder letter Q3 2023 2023, retrieved 2025-10-02^
- Brendyn Lotz. Duolingo kicks contractors out the door while chasing the shadow of AI April 29, 2025, retrieved 2025-10-01^
- Brendyn Lotz. Duolingo CEO tries to walk back AI-first comments, fails May 26, 2025, retrieved 2025-10-01^
- Lauren Hockenson. Duolingo snags iPhone App of the Year Gigaom, 2013-12-17, retrieved 2014-02-21^
- Luis. Duolingo turns two today! retrieved 2014-11-21^
- Rip Empson. Fast-Growing Duolingo Caps Off a Big Year with the Crunchie for 'Best Education Startup' TechCrunch, 2014-02-12, retrieved 2023-10-06^
- Abhimanyu Ghoshal. Google Play reveals the most downloaded apps, games and entertainment content from 2014 The Next Web, 2014-12-11, retrieved 2014-12-29^
- Duolingo theindexproject.org, retrieved 2023-10-06^
- Building character: How a cast of characters can help you learn a language Duolingo Blog, 2020-11-10, retrieved 2024-08-24^
- Duolingo. Creating Our Duolingo Characters • Greg Hartman • Duocon 2020 2020-09-26, retrieved 2024-07-24^
- at Duolingo Blog How Zari, Bea, Lily, Lucy, and Lin came to life Duolingo Blog, 8 March 2022, retrieved 26 September 2024^
- Madeline Bartos. Duolingo Owl is dead, company says - CBS Pittsburgh CBS News, 2025-02-12, retrieved 2025-02-14^
- Duo, the Duolingo owl, has 'died' - leaving users in mourning (and somewhat relieved) The Independent, 2025-02-13, retrieved 2025-02-14^
- Callum Booth. Duolingo Owl Dies—But 'The Dead Internet Theory' Lives On Forbes, 2025-02-12, retrieved 2025-02-14^
- Saba Hamedy. Duolingo 'killed' off its mascot — and somehow captivated the internet NBC News, 2025-02-12, retrieved 2025-02-15^
- Greta Cross. Duolingo's make-believe owl mascot Duo dies by Cybertruck in new TikTok USA TODAY, retrieved 2025-02-15^
- Omar Gallaga, Gael Cooper. Duolingo Is Selling a Coffin for Dead Mascot Duo the Owl CNET, 2025-02-14, retrieved 2025-02-15^
- Greta Cross. Duolingo's make-believe mascot, Duo the Owl, duped his death The News Journal, retrieved 2025-02-25^
- Duolingo Resurrects Its Mascot After Viral Cybertruck Death www.designrush.com, February 25, 2025, retrieved 2025-02-25^
- Greta Cross. Duolingo announces death of Duo the Owl, its make-believe mascot: 'He had many enemies' USA TODAY, retrieved 2025-02-14^
- Brooke Steinberg. Duolingo announces the death of its beloved owl mascot, Duo New York Post, 2025-02-12, retrieved 2025-02-14^
- Brand Guidelines - Duolingo design.duolingo.com, retrieved 2025-02-12^
- Sage Anderson. The Duolingo owl is out for vengeance in these threatening memes. Mashable, 2019-03-27, retrieved 2019-06-07^
- Alice Gibbs. Threatening note from the Duolingo owl leaves internet in stitches Newsweek, 2023-12-05, retrieved 2024-06-25^
- Sunil Bajaj. How a 23-year-old graduate helped transform Duolingo's social media marketing Contagious, November 23, 2023, retrieved 13 April 2024^
- Introducing Duolingo Push Duolingo, 2019-03-31, retrieved 2019-06-07^
- How Duolingo Took over the Meme World and What Marketers Can Learn from It rypl.io, April 30, 2019, retrieved 2019-06-07^
- Lawyer Fights Duolingo Owl for $2,700,000 Duolingo, April 1, 2022, retrieved 13 April 2024^
- Spanish or Vanish (full song) from Duolingo On Ice Duolingo, April 2024, retrieved 13 April 2024^
- Madasyn Lee. Pittsburgh-based Duolingo a fan of talk-to-kids 'SNL' sketch Pittsburgh Tribune-Review, 2019-11-05, retrieved December 13, 2019^
- Aakanksha Agarwal. Duolingo's viral taco shop pulls in $700k in first year Technical.ly, 2024-06-12, retrieved 2024-08-24^
- Diana Budds. Inside Duolingo's stunning new NYC office, where employees get to choose where and how they work Fast Company, September 5, 2024, retrieved September 5, 2024^
- Duolingo Path. Duolingo Opens New Office in NYC 2024-09-07, retrieved 2024-09-07^
- Duolingo Careers careers.duolingo.com, retrieved 2024-11-03^
- Nilay Patel. Duolingo CEO Luis von Ahn thinks AI has a lot to teach us The Verge, 2024-10-14, retrieved 2024-11-02^