An essential reference tool with an informative introduction to the system. Part 1 is the reference manual to the C Language X Interface Library, or XLib for short. It presents an overview of the system, explains how to create and manipulate windows, gives an in-depth look at graphics capabilities, and explains events, event-handling functions, and a variety of utility functions. Part 2 is a detailed specification of the X protocol semantics with an appendix defining the precise encoding. It is independent of any one programming language and can be used as a starting point for creating interface libraries for other programming languages. Instructive diagrams and a comprehensive technical index add to the book's usefulness.