I got in Parkour about a year ago and was looking for something to help supplement my training.
This book was just what I was looking for and more!
What I asbolutely loved were the detailed breakdowns...complete with pictures, descriptions and pointers...on performing specific moves. It also has a practical section for troubleshooting each move along with some of the possible fixes. For instance, if your feet scrape the top of an obstacle during a kong vault, lower your center of gravity during approach, take off closer to the wall, etc...
The book also covers some basic training habits, fitness tip and warm-up exercises. Out side of "How To" areas are sections covering the history and origin or Parkour, the differences between it and Freerunning and some interviews with some of the top Traceurs around. There's also a neat section on setting up a Parkour education cirriculum.
As with any sport or martial art, nothing can take the place of constant practice. But every so often, it's good to get behind the moves and approach the practice systematically and intellectually.
Whether you're a beginner or a Master Traceurs, this book is the best tool around to help sharpen the mental aspect of your Parkour practice.