Duolingo is a free, science-based language education platform that has organically become the most popular way to learn languages online. Duolingo has given Chris permission to share some of their research around the gamification of their app. In this talk, Chris reveals the secrets behind game mechanics that foster effective learning, high user retention, and revenue generation – in a free app. A German native, Chris received his MSc in Computer Science from the University of Koblenz–Landau.