Leaflet, a JavaScript library for mobile-friendly interactive maps, has come a long way since its inception. The library started as a one-night hack and evolved over the next two years as a closed proprietary API, developed by one person, and then was finally rewritten from scratch as an open source library in 2011. Leaflet is now the most popular open source solution for publishing maps on the Web. What’s the story behind Leaflet? How did it became so successful so quickly despite strong competition and lack of features? This talk will be presented by its lead developer and will cover lessons learned, the current state of the project and future challenges.