SML is an influential programming language that represents many state-of-the-art aspects of language design in a form usable for everyday programming. The language is in use worldwide, with applications ranging from network communication to theorem proving. The definition for SML's standard library, this work concisely describes the types and functions defined in the library and discusses in depth the library's design and use. This manual will be an indispensable reference for students, professional programmers, and language designers.