An introduction to compiling to WebAssembly, from a low-level perspective. Learn more about the nuts and bolts of targetting basic WebAssembly 1.0, as well as a look forward towards extensions that are still in development. Let Andy guide you through the general shape and the low-level details of WebAssembly as a compiler target. As a significant contributor to Firefox's WebAssembly implementation, Andy is in a good position to know what you can ship in practice, as well as what you might expect to be able to ship in a year or in two years. He has also written compilers that exercise more experimental features, such as integration with host garbage collectors, tail calls, and more. His experience working on the WebAssembly backend of LLVM has also been illuminating in ways not limited to compiling C and C++ programs.