Book excerpt: Here is a thorough and authoritative guide to the latest version of the S language and its programming environment. Programming With Data describes a new and greatly extended version of S, written by the chief designer of the language itself. It is a guide to the complete programming process, starting from simple, interactive use, and continuing through ambitious software projects. The focus is on the needs of the programmer/user, with the aim of turning ideas into software, quickly and faithfully. The new version of S provides a powerful class/method structure, new techniques to deal with large objects, extended interfaces to other languages and files, object-based documentation compatible with HTML, and powerful new interactive programming techniques. This version of S underlies the S-Plus system, versions 5.0 and higher.