Whitewater Kayaking is the most comprehensive and valuable book about the sport. It draws on the combined 30+ years experience of world-renowned paddlers and instructors, Ken Whiting and Kevin Varette, and covers everything from the most basic skills and concepts to the most advanced, cutting edge paddling techniques.
Not many books available on this subject (probably best to learn from an instructor anyways). I was looking more for a book that would help me move through moderate rapids in my (14') jack-of-all trades kayak. This book is exclusively focused on the much smaller, special-purpose whitewater boats, so some of the information in it was useful to me, whereas other techniques don't translate to a larger boat.