Explore Duolingo's journey from zero revenue to becoming the top-grossing education app in this 34-minute conference talk from Sustainable Growth Day '19. Learn how Duolingo built a revenue growth engine with Duolingo Plus while staying true to their mission of making language education free, fun, and accessible to all. Discover the experimentation strategies, key features, and emotional elements that contributed to their success. Gain insights from Duolingo's Chief Revenue Officer and Director of Product Management as they discuss various experiments, including the streak feature, offline capabilities, and the introduction of Duo's voice. Understand how Duolingo balances monetization with their core principles and get a glimpse of upcoming products. Conclude with a Q&A session and community engagement opportunities.