Agile Retrospectives: Making Good Teams Great by Esther Derby and Diana Larsen is the best book ever written on running agile retrospectives.
If you've read it, then you know exactly what I'm talking about.
But if you haven't, here's why:
Reason #1: It tells you exactly how to run a great retrospective
This book gets right to the point and explains step-by-step how to run great retrospectives.
Reason #2: It includes great activities
A lot of teams run the same retrospective format over and over. But this book gives you a handful of tried and true activities so that your team won't get bored.
Reason #3: It discusses what might go wrong
It's one thing to read about doing something, it's another to try it in practice. And anyone who's run a retrospective knows it can quickly go off the rails.
But this book will help you navigate things going "wrong."
Reason #4: It explains "why"
Most teams just go through the motions when doing retrospectives. But understanding why they are so important will totally change how you approach running them.
I can't recommend this book enough.