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Duolingo is an American language-learning website and mobile app and a digital language proficiency assessment exam. The company uses the freemium model: the app and the website are accessible without charge, although Duolingo also offers a premium service for a fee.

As of March 2021, the language-learning website and app offer 106 different language courses in 38 languages. The app has over 300 million registered users across the world.


The project was initiated at the end of 2009 in Pittsburgh by Carnegie Mellon University professor Luis von Ahn and his graduate student Severin Hacker.

The inspiration for Duolingo came from two places. Luis von Ahn wanted to create a program that served two purposes in one program. Duolingo originally achieved this by teaching its users a foreign language while having them translate simple phrases in documents, though the translation feature has since been removed.

Von Ahn was born in Guatemala. He saw how expensive it was for people in his community to learn English. Severin Hacker (born in Zug, Switzerland), co-founder of Duolingo and current CTO, and von Ahn believed that “free education will really change the world and wanted to supply people with an outlet to do so.

The project was originally sponsored by Luis von Ahn’s MacArthur fellowship and a National Science Foundation grant.

On October 19, 2011, Duolingo raised $3.3 million from a Series A first round of funding, led by Union Square Ventures, with participation from author Tim Ferriss and actor Ashton Kutcher‘s firm, A-Grade Investments.

Duolingo launched into private beta a month later on November 30, 2011, and accumulated a waiting list of more than 300,000 users.

On June 19, 2012, Duolingo later launched for the general public.

On September 17, 2012, Duolingo raised $15 million from a Series B second-round of funding led by New Enterprise Associates, with participation from Union Square Ventures bringing Duolingo’s total funding to $18.3 million.

On 13 November 2012, Duolingo released their iOS app through the iTunes App Store. The application is a free download and is compatible with most iPhoneiPod and iPad devices.

On 29 May 2013, Duolingo released their Android app, which was downloaded about a million times in the first three weeks and quickly became the #1 education app in the Google Play store.

On June 19, 2013, one year after launching for the general public, Duolingo passed 4 million users, all through word of mouth, and on November 21, 2013, Duolingo reached 15 million users.

On February 18, 2014, Duolingo raised $20 million from a Series C round of funding led by Kleiner Caufield & Byers. Duolingo had about 25 million registered users, 12.5 million active users, and 34 employees. On June 2, 2014, Duolingo passed 30 million users.

On June 10, 2015, Duolingo raised $45 million from a Series D fourth-round of funding led by Google Capital, bringing its total funding to $83.3 million, a valuation of $470 million, as well as passing 100 million users.

In April 2016, it was reported that Duolingo had 17 million monthly users.

On July 25, 2017, Duolingo raised $25 million from a Series E fifth-round of investment from Drive Capital, bringing its total funding to $108.3 million, a valuation of $700 million, and passing 200 million users and having 25 million monthly users. It was reported that Duolingo had 95 employees, and the funds would be directed toward creating initiatives such as TinyCards and Duolingo Labs.

On August 1, 2018, it was reported Duolingo had passed 300 million users.

On December 4, 2019, it was announced that Duolingo raised $30 million in a Series F sixth-round of investment from Alphabet’s investment company CapitalG, bringing total funding of $138.3 million, a valuation of $1.5 billion, reporting 30 million monthly active learners. Duolingo will use the funds on developing new products and expanding its team. Expanding the team will span a variety of positions, including in engineering, business development, design, curriculum and content creators, community outreach and marketing.

During 2019, Duolingo grew from 170 staff members to 200 employees, with headquarters in the Pittsburgh neighbourhood of East Liberty and offices in New YorkBellevue Washington (near Seattle); and Beijing.[40][49] Of Duolingo’s 199 employees, 165 work in its East Liberty headquarters, 17 work in New York, 8 in Bellevue, and 8 in China.

Duolingo had revenue of $1 million in 2016, $13 million in 2017, $36 million in 2018, and was projected to hit $86 million in 2019. In April 2020, Duolingo passed one million paid subscribers.


Duolingo mimics the structure of video games in several ways to engage its users. It features a reward system in which users acquire “lingots” or gems, an in-game currency that they can spend on features such as character customizations or bonus levels (both available on the mobile app only).

On public leaderboards, people can compete against their friends or see how they stack up against the rest of the world in randomly selected groupings of up to 30 users. The level system that Duolingo uses is XP (experience points), a numerical system that represents a user’s skill level. Badges in Duolingo represent achievements that are earned from completing specific objectives or challenges.

The study process in Duolingo combines various methods such as: listening to the pronunciation, reading sentences, voice recording, forming phrases by ordering words, and matching images to words.

Use in schools

Duolingo provides “Duolingo for Schools” with features designed to allow teachers to track students’ progress. In 2012 an effectiveness study concluded that Duolingo usage for Spanish study was more effective than classroom language-learning alone, but that Duolingo was less effective for advanced language learners. One proposed reason for this is that the grammar-translation method that Duolingo primarily uses is more applicable to simple words and phrases than to complex ones; simpler ones can translate more precisely from one language to another and thus are more conducive to Duolingo’s grammar-translation method.


Duolingo Incubator is a platform where volunteers can participate and contribute to creating new language courses for Duolingo. A volunteer willing to participate must be a registered Duolingo user and has to go through the application process before contributing to a particular course they are interested in. This initiative allowed Duolingo to create more courses hence increasing their community to reach the maximum potential of the language learners.

Business model

Most language-learning features in Duolingo are free of charge, but it has periodic advertising in both its mobile and web browser applications, which users can remove by paying a subscription fee. This feature, ‘Duolingo Plus’, includes benefits such as unlimited hearts, level skipping, and progress quizzes. It originally employed a crowdsourced business model, where the content came from organizations (such as CNN and BuzzFeed) that paid Duolingo to translate it.


Duolingo utilizes many services in the Amazon Web Services suite of products, including Amazon DynamoDBAmazon Virtual Private Cloud, nearly 200 virtual instances in Amazon Elastic Compute Cloud (EC2), Amazon Simple Storage Service (S3) and Amazon Relational Database Service (RDS). The server backend is written in the programming language Python. A component called the Session Generator was rewritten in Scala by 2017. The frontend was written in Backbone.js and Mustache but is now primarily in React and Redux. Duolingo provides a single-page web application for desktop computer users and also smartphone applications on Android (both Google Play Store and Amazon Appstore) and iOS App Store platforms. 20% of traffic comes from desktop users and 80% from mobile app users.

Recognition and awards

In 2013, Apple chose Duolingo as its iPhone App of the Year, the first time this honour had been awarded to an educational application. Duolingo won Best Education Startup at the 2014 Crunchies and was the most downloaded app in the Education category in Google Play in 2013 and 2014. In 2015, Duolingo has announced the 2015 award winner in the Play & Learning category by Design to Improve Life.

Duolingo was named No. 44 on Fast Company‘s “The World’s 50 Most Innovative Companies” list in 2018 “for making new languages irresistible”. No. 2 on Fast Company‘s “The World’s Most Innovative Companies: Education Honorees” in 2018 “for making a new language irresistible”, and No. 2 on Fast Company‘s “The World’s Most Innovative Companies: Education Honorees” in 2017 “for letting friends compare notes as they learn a new language”. No. 6 on Fast Company‘s “The World’s Most Innovative Companies: Social Media Honorees” in 2017 “for letting friends compare notes”. No. 7 on Fast Company‘s “The World’s Most Innovative Companies: Education Honorees” in 2013 “for crowdsourcing web translation by turning it into a free language-learning program”.

Duolingo won Inc. magazine’s Best Workplaces 2018, Entrepreneur magazine’s Top Company Culture List 2018, and appeared in CNBC‘s 2018 and 2019 “Disruptor 50” lists. TIME Magazine’s 50 Genius Companies. In 2019, Duolingo was named one of Forbes’s “Next Billion-Dollar Startups 2019”.


Duolingo has received criticism for its lack of effectiveness in helping students to fully learn a language. Duolingo’s CEO, Luis von Ahn, promises only to get users to a level between advanced beginner and early intermediate, saying “A significant portion of our users use it because it’s fun and it’s not a complete waste of time.” After six months of studying French with Duolingo, von Ahn demonstrated a lack of basic verb tenses when asked to describe his weekend in French, “mangling his tenses.” Bob Meese, Duolingo’s chief revenue officer, did not immediately understand the spoken question “¿Hablas español?” (“Do you speak Spanish?” in Spanish) after six months of Duolingo Spanish language study.

Language coach and podcaster Kerstin Cable has criticized the app for “its impractical vocabulary, its insistence upon one acceptable translation per sentence prompt, and its lack of explanation for incorrect answers,” describing Duolingo’s method as “[learning] by parroting phrases without even beginning to cover the background stories that grammar and pragmatics tell.” Linguist Steven Sacco at San Diego State University attempted to test Duolingo’s claim that “34 hours of Duolingo are equivalent to a full university semester of language education” by completing a course in Swedish, and taking a standardized elementary exam, ultimately receiving a failing grade. Sacco suggested that Duolingo helps learn vocabulary only in addition to immersion environments like a classroom. Both Sacco and Cable added that Duolingo’s translation method of teaching is ultimately inferior to learning a language in an immersion environment.

Duolingo has also received criticism for its treatment of its courses’ contributors, who work entirely on a volunteer basis. With the company transitioning to what could be considered a more revenue-focused business approach, the public backlash caused the app to fall out of favour with many people and even prompted one of the contributors to the Norwegian course to leave after having contributed to the course for six years, as well as managing the user forum and providing resources for the language. This left an in-development addition to the Norwegian course unreleased for the site’s users. While the exact reason for her departure was left unspecified, a lack of respect for the volunteer work from which the site profits was mentioned. While some contributors to Duolingo’s larger courses (e.g. Spanish and French for English speakers) receive a salary, users speculate that the contributors’ volunteer work allows for a greater degree of autonomy than that of an employee, which was subsequently threatened by Duolingo’s changing business model.

In popular culture

Duolingo’s mascot, a green cartoon owl named Duo, has been a subject of an Internet meme in which the mascot will stalk and threaten users if they do not keep using the app. Acknowledging the meme, Duolingo released a video on April 1, 2019; the video depicts a new feature called “Duolingo Push”. In the video, users of “Duolingo Push” will receive reminders to use the app in person by Duo himself, who stares at users and follows them around until they use the app (in the video, Duo is depicted by a person in a large mascot costume).

In November 2019, Saturday Night Live parodied Duolingo in a skit where adults learned to communicate with children using a fictitious course on the app titled “Duolingo for Talking to Children.