WebAssembly is a fast, portable, compact, cross-browser binary format for compilation to the Web. It allows new types of applications and heavy 3D games to run efficiently in browsers. We'll describe what web assembly is, the problems it solves, the low level format and compilation tools available to try it out. In addition, the interfacing between compiled language modules and Javascript is explained. Video: https://www.youtube.com/watch?v=6v4E6oksar0