This is also known as the "white book". It is the first edition of the foundational book about XP, the preferred by the purist extreme programmers.
Robert Cecil Martin (aka Uncle Bob) - Agile Software Development, Principles, Patterns, and Practices
Despite extreme programming is not mentioned in the title, this book could be used as a practical guide to applying most of the XP Practices. In this edition code examples are in Java and C++
This edition has C# code examples. The topics are the same as the first edition.