|Type of business||Privately held company|
|Headquarters||Pittsburgh, Pennsylvania, United States|
|Founder(s)||Luis von Ahn, Severin Hacker|
|CEO||Luis von Ahn|
|Industry||Online education, Professional certification, Translation, Crowdsourcing|
|Services||Language courses, Duolingo English Test, Duolingo for Schools, Tinycards flashcard app|
|Revenue||$ 36 million USD in 2018|
|Users||>300 million users|
|Launched||30 November 2011 (private beta)|
19 June 2012 (public release)
|Native client(s) on||Android, iOS, Windows Phone, Windows 10 Mobile|
Duolingo (/ -, -/, D(Y)OO-oh-LING-goh) is an American language-learning website and mobile app, as well as 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.
The project was initiated at the end of 2009 in Pittsburgh by Carnegie Mellon University professor Luis von Ahn (creator of reCAPTCHA) and his graduate student Severin Hacker, and then developed along with Antonio Navas, Vicki Cheung, Marcel Uekermann, Brendan Meeder, Hector Villafuerte, and Jose Fuentes.
The inspiration for Duolingo came from two places. Luis von Ahn wanted to create a program that served two purposes in one, what he calls a "twofer". 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 an outlet to do so.
On October 19, 2011, during in its "Early Stage Venture" stage 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 
On June 19, 2012, Duolingo later launched for the general public.
On September 17, 2012, while still in its "Early Stage Venture" stage, 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 February 18, 2014, Duolingo entered its "Late Stage Venture" stage, and raised $20 million from a Series C third-round of funding led by Kleiner Caufield & Byers. It was reported Duolingo had 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.
On July 25, 2017, that 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, as well as 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 a 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 neighborhood of East Liberty and offices in New York; Bellevue, Washington (near Seattle); and Beijing. Of Duolingo’s 200 employees, 166 work in its East Liberty headquarters, 17 work in New York, 8 in Bellevue, and 8 in China.
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 crowd sourced business model, where the content came from organizations (such as CNN and BuzzFeed) that paid Duolingo to translate it.
Duolingo Incubator  is a platform where volunteers can participate and contribute to create new language courses for Duolingo. Volunteers 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 in order to reach the maximum potential of the language learners.
Duolingo: Incubator consists of three main phases. They are the following -
Phase 1 - This is the phase where contributors would work on building a new language course with different lessons, modules, activities, and examples. This is the most initial stage of the Incubation and contributors would be working from scratch to make the language course fully functional and understandable for the new users.
Phase 2 - This is the phase where Duolingo would release the particular course as a Beta Version. This would allow beta testers to review the course and give feedback about it. Feedbacks from the beta version would make the contributors make more changes before finally releasing it completely.
Phase 3 - This is the phase where Duolingo would completely release the course to its all users after passing the beta test. These courses are fully accessible to its users on digital platforms. There are over 70 language courses in this phase.
Duolingo uses many services in the Amazon Web Services suite of products, including Amazon DynamoDB, Amazon 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.[better source needed] 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 smart phone applications on Android (both Google Play Store and Amazon Appstore), iOS App Store and Windows Phone platforms. 20% of traffic comes from desktop users and 80% from mobile app users.
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 2013, Apple chose Duolingo as its iPhone App of the Year, the first time this honor 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 was announced the 2015 award winner in 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 mimics the structure of video games in several ways in order to engage its users. It features a reward system in which users acquire "lingots", 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. 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.
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 in a more exact manner from one language to another and thus are more conducive to Duolingo's grammar-translation method.
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: "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?" after six months of Duolingo Spanish study.
Language coach and podcaster Kersten 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 "you learn 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 of "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 some use for Duolingo as helpful for learning 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.
As of June 24, 2020[update], 36 courses are available to the public in English, three of which are constructed languages, including two fictional languages. In this list, the courses are ordered by number of active learners.
As of June 28, 2020, 23 languages are available to speakers of languages other than English.