This is the book I use the most when I need agile techniques for my projects. It contains all the info you need from a managers perspective; when you need a technique, and how to apply. I am very happy with all the fundamental explanations on why certain techniques can help you out with a project problem. Stakeholder participation, requirements, testing, development strategies, it is all in there. And best of all, without hype.
My favorite chapter is "Stealth Methodology Adoption" which explains how to sell to higher level management that you are going agile.
With contributions from Scott Ambler, Alistair Cockburn, Larry Constantine and Ronald Jeffries you know that the advice presented is from real experts.