Common LISP. The Language. Second Edition

This is the Lisp programmers' bible. If you need to know the official specification, every function defined in Common Lisp can be found in here somewhere. Anyone vaguely serious about programming in Lisp for extended periods of time should keep a copy of this book for reference. However, note that while this book is clearly written, it is not an introduction to programming in Lisp--Common Lisp: The Language only offers the language specification.