WebAssembly: The Definitive Guide provides a thorough and accessible introduction to one of the most transformative technologies hitting our industry. What started as a way to use languages other than just JavaScript in the browser has evolved into a comprehensive path toward portability, performance, increased security and greater code reuse across an impressive collection of deployment targets. The goals may sound familiar, but in practice, we’re finally getting our safe, fast, portable, and secure software development environment offering the potential for reuse. This practical book introduces the elements of this technology incrementally while building to several concrete, code-driven examples of practical but cutting edge WebAssembly uses.