Duolingo was founded in 2011 by Luis von Ahn and Severin Hacker. What started as a side project in a Carnegie Mellon University computer science class, quickly turned into a full-fledged mobile app that aimed to make language learning more accessible and engaging for people all around the world.

When Duolingo first launched, it had a small team of developers and only a few thousand users. However, as smartphones became more prevalent and app stores grew in popularity, Duolingo’s user base began to grow rapidly. By the time the app launched on iOS in 2012, it had over 300,000 users.

Duolingo’s success is driven by it’s game-like style and short lessons that make learning a new language fun and easy to fit into a busy schedule, which really helped with its popularity.

In 2018, Duolingo reached over 300 million users worldwide and offers lessons in over 30 languages. The company has also expanded beyond its original mobile app, with the launch of Duolingo for Schools and Duolingo for Business. The company is valued at over $1 billion and has raised over $108 million in funding.

It's hard to believe that Duolingo started as a small side project in a university computer science class. Today it’s one of the most popular language-learning apps and a household name for many people around the world.