Duolingo

Duolingo, Inc. is an American educational technology company that produces learning apps and provides language certification. Duolingo offers courses on music, math, and 43 languages, ranging from English, French, and Spanish to less commonly studied languages such as Welsh and Irish. Other services include the Duolingo English Test, an online language assessment, and Duolingo ABC, a literacy app for children. The company uses a freemium model, with its optional premium services, Super Duolingo and Duolingo Max, being ad-free and offering more features.

, Duolingo was the world's most popular language learning app based on monthly downloads, with around 16.2 million users downloading it that month. A systematic review of research on Duolingo from 2012 to 2020 found comparatively few studies on the platform's efficacy for language learning, but the review identified several studies that reported relatively high user satisfaction and enjoyment and positive perceptions of the app's effectiveness. The company is often recognized for its successful marketing tactics.

Early history
The idea for Duolingo was formulated in 2009 by Carnegie Mellon University professor Luis von Ahn and his Swiss-born post-graduate student Severin Hacker. Von Ahn had sold his second company, reCAPTCHA, to Google and, with Hacker, wanted to work on an education-related project. 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. The Duo mascot is a green owl because co-founder Severin Hacker hates the color green.

The project was originally financed by von Ahn's MacArthur fellowship and a National Science Foundation grant. 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.

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. Duolingo launched a private beta on November 27, 2011, and accumulated a waiting list of more than 300,000 people. It launched to the general public on June 19, 2012, at which point the waiting list had grown to around 500,000.

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. In November 2012, Duolingo released an iPhone app, followed by an Android app in May 2013, at which time Duolingo had around 3 million users. By July 2013, it had grown to 5 million users and was rated the No. 1 free education app in the Google Play Store.

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. At this time, it had 34 employees, and reported about 25 million registered users and 12.5 million active users; it later reported a figure closer to 60 million users.

In June 2015, it 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. In April 2016, it was reported that Duolingo had more than 18 million monthly users.

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. It was reported that Duolingo had 95 employees. 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. On August 1, 2018, Duolingo surpassed 300 million registered users.

In December 2019, it was announced that Duolingo raised $30 million in a Series F funding round from Alphabet's investment company, CapitalG. 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. 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.

Features and media
In October 2013, Duolingo launched a crowdsourced language incubator. In March 2021, it announced that it would be ending its volunteer contributor program and donating money to its volunteer contributors who helped develop it. The company said that from now on, language courses would be maintained and developed by professional linguists aligning with CEFR standards. On June 28, 2021, Duolingo filed for an initial public offering on NASDAQ under the ticker DUOL. From August 2021 to June 2022, the Duolingo language learning app was removed from some app stores in China.

In the early-2020s, Duolingo was noted for its viral videos on the social media platform TikTok.

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 Twitter. CEO Luis von Ahn stated that there were no plans to reverse the changes—intended to simplify Duolingo for its new users—maintaining both the old and new versions would be difficult. In October 2022, Duolingo acquired Detroit-based animation studio Gunner; it is the studio that produces art assets and animation for Duolingo and Duolingo ABC and its marketing campaigns. In October 2023, Duolingo released math and music courses in English and Spanish for iOS users.

In March 2023, Duolingo officially announced the planned Duolingo Max, a subscription tier above Super Duolingo, in their blog. In July 2023, Duolingo launched a feature using the iOS widget feature. In January 2024, after having laid off around ten percent of its contractors, Duolingo began using artificial intelligence (AI) to replace tasks usually done by its contractors. In March 2024, the widget feature was also on Android.

In 2024 Duolingo acquired Detroit-based design studio Hobbes.

Duolingo
Duolingo is an app and website that uses a gamified approach to language learning, with lessons that incorporate translating, interactive exercises, quizzes, and stories. It also uses an algorithm that adapts to each learner and can provide personalized feedback and recommendations.

Duolingo has been through many design phases. Formerly, it provided users with different "skills" placed along a "tree", where they could progress by completing every skill above them. The user could upgrade the skill at any time, with the final goal of turning it "golden" or "legendary". In November 2022, Duolingo switched to an AI-assisted path, where the user's learning level is put on a single "path", including the stories. After its switch to this new format, it removed the audio-only lessons it had offered for some languages. Duolingo also provides a competitive space, such as in Leagues, where people can compete against their friends or see how they compare with randomly selected worldwide player groupings of up to 30 users. Rankings in Leagues are determined by the amount of "XP" (experience points) earned in a week. Badges in Duolingo represent achievements earned from completing specific objectives or challenges.

Duolingo provides features that allow teachers to track their students' progress.

Duolingo currently offers the following language courses:
 * Arabic
 * Catalan
 * Chinese (Cantonese)
 * Chinese (Mandarin)
 * Czech
 * Danish
 * Dutch
 * English
 * Esperanto
 * Finnish
 * French
 * German
 * Greek
 * Guarani
 * Haitian Creole
 * Hawaiian
 * Hebrew
 * High Valyrian
 * Hindi
 * Hungarian
 * Indonesian
 * Irish
 * Italian
 * Japanese
 * Klingon
 * Korean
 * Latin
 * Navajo
 * Norwegian
 * Polish
 * Portuguese
 * Romanian
 * Russian
 * Scottish Gaelic
 * Spanish
 * Swahili
 * Swedish
 * Turkish
 * Ukrainian
 * Vietnamese
 * Welsh


 * Yiddish
 * Zulu

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.

Duolingo has a widget feature on iOS and Android. The widget feature initially started as Duolingo's annual hackathon project. The iOS widget has 39 illustrations designed by Kyle Ruane that were intended to be another daily reminder to complete lessons. On the top part of the widgets is the user's daily streak. On the Duolingo Blog, they wrote that they "decided to come up with a series of illustrations that would show Duo’s mood at different parts of the day". Any lesson completed in Duolingo will count towards the user's daily streak. The daily streak 's visual symbol in the app is fire.

The company owns a blog called Duolingo Blog that publishes self-data reports of the common language selected in the Duolingo app.

Subscriptions
Most of Duolingo's language-learning features are free, with periodic advertising in its mobile and web browser applications, which users can remove by paying a subscription fee or promoting referral links. This program, known as Super Duolingo, includes benefits such as unlimited hearts (retries), level-skipping, no ads, and progress quizzes.

Duolingo Max is a subscription above Super Duolingo. It uses GPT-4 for its features: Role Play, an AI conversation partner, and Explain My Answer, which breaks down the rules with a modified GPT-4 when the user makes a mistake. It is available on the iOS version of the Duolingo app in Australia, Canada, Ireland, New Zealand, the United Kingdom, and the United States in French and Spanish for English speakers. It was intended for immersion—as in "to have a free-flowing conversation".

Duolingo ABC
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.

Duolingo Math
Duolingo Math is an app course for learning elementary mathematics. It was announced on YouTube on August 27, 2022, at the Duocon 2022 event.

Duolingo Music
In March 2023, Duolingo was reportedly developing a new music course that would allow users to learn how to read and play music through its gamified learning experience. On October 11, 2023, Duolingo formally unveiled Duolingo Music in a YouTube Short, a new platform within the existing app that provides basic music learning through piano, drums, and sheet music lessons. As of April 2024, it is currently available on iOS and Android devices.

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. The test's certificate is 'accepted' by over 5,000 programs internationally, though some schools do not 'accept' the certificate.

Business model
Duolingo had revenue of $1 million in 2016, $13 million in 2017, $36 million in 2018, and $250.77 million in 2021. In May 2022, it was reported that 6.8% of its monthly active users paid for the ad-free version of the app. Duolingo has derived most of its revenue from subscriptions, advertising, and its Duolingo English Test. In April 2020, it passed one million paid subscribers; it reached 2.9 million in March 2022, and 4.8 million at the end of March 2023.

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. A 2022 study on adults using Duolingo as their only language learning tool, published in the journal Foreign Language Annals, found that the participants that 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. Another 2022 study of Malaysian students learning French, published by the National University of Malaysia Press, found that it facilitated the acquisition of vocabulary and concluded that it was "well suited" for beginners in this regard.

According to Duolingo's own 2021 study, five semesters of university instruction are roughly equivalent to five sections of the app, and Duolingo is an "effective tool [...] at an intermediate level". A 2023 study funded by Duolingo concluded that Duolingo English learners did not significantly learn much grammar. Duolingo English learners in Colombia and Spain were found to gain significantly more proficiency than students in a classroom, except for listening.

Criticism
Some language professionals have criticized its app for its limitations and gamified design. Others have pointed out that Duolingo and similar apps can be a starting point but lack the human interaction required to be fluent in a language and for real-life conversations. Players have also reported that "gamification" has led to cheating, hacking, and incentivized game strategies that conflict with actual learning. Duolingo's study conclusion has been criticized for being "a meaningless assertion."

In March 2022, Duolingo forums were discontinued, and users will no longer be able to participate in Sentence Discussions. The change has been criticized on some online sites, such as Reddit.

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". They concluded that the data was obtained by scraping publicly available information based on an exposed application programming interface (API). Duolingo's spokesperson states that the API is intentionally publicly visible.

Since the end of October 2023, Duolingo has decided to stop updating its Welsh course to "focus on languages in higher demand". Some users criticize 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.

Awards
In 2013, Apple chose Duolingo as its iPhone App of the Year, a first for an educational application. That year, Duolingo ranked No.7 on Fast Company "The World's Most Innovative Companies: Education Honorees" list "for crowdsourcing web translation by turning it into a free language-learning program". Duolingo won Best Education Startup at the 2014 Crunchies, and was the most downloaded 'education app' in Google Play in 2013 and 2014. In July 2020, PCMag named it "The Best Free Language Learning App".

As a company, Duolingo has likewise won several awards and recognitions. In 2015, it was announced as that year's Index Award winner in the Play & Learning category by The Index Project. It won Inc. magazine's Best Workplaces 2018, made Entrepreneur magazine's Top Company Culture List 2018, was among CNBC's "Disruptor 50" lists for 2018 and 2019,  and was ranked as one of TIME magazine's 50 Genius Companies. Duolingo was named one of Forbes "Next Billion-Dollar Startups 2019". In 2023, Duolingo won a Design Award during the 2023 edition of the Apple Design Awards.

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 where the mascot is "evil" and stalks and threatens users if they do not keep using the app.

Duolingo has leaned into its online reputation and has adjusted its social media and marketing strategies accordingly. 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. 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. 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." In February 2020, as part of the company's partnership with Angry Birds 2, a skit video depicting Duo and the red Angry Bird attacking people was uploaded.

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".

The 2023 film Barbie contains a running gag where the husband of disgruntled Mattel employee Gloria uses Duolingo to learn Spanish, Gloria's native language.