This fast-moving tutorial introduces you to OCaml, an industrial-strength programming language designed for expressiveness, safety, and speed.Through the book's many examples, you'll quickly learn how OCaml stands out as a tool for writing fast, succinct, and readable systems code using functional programming.Real World OCaml takes you through the concepts of the language at a brisk pace, and then helps you explore the tools and techniques that make OCaml an effective and practical tool.You'll also delve deep into the details of the compiler toolchain and OCaml's simple and efficient runtime system.This second edition brings the book up to date with almost a decade of improvements in the OCaml language and ecosystem, with new chapters covering testing, GADTs, and platform tooling.This title is also available as open access on Cambridge Core, thanks to the support of Tarides.Their generous contribution will bring more people to OCaml.