Mountain Biking The Manual does what it says on the tin. It is absolutely packed with information. In 255 pages it covers subjects like a brief history of mountain biking, equipment, training, psychology, crashing, recovery and competition. And that's just to start with. The meat for me is the mountain biking technique. It's all in there, from the basics including body position, flat corners, berms, rocks, roots, pumping and flow right up to getting air, manuals, bunny hops, flips and tail whips. 

What I like about his book is that it covers so many topics but it never feels like a chore to read because each section is quite short. You can read it cover to cover, or dip in and out. Importantly it's very well written. The author, Chris Ball, is very good at breaking down the essentials of each technique so they can be understood and be applied on the trail. I learnt so much from this book on the first read, and have come back to it again and again when I need a refresher on something. 

I do have one complaint. However good your prose is, sometimes what you're trying to explain is much clearer if you use a diagram. Mountain Biking The Manual would definitely benefit from some diagrams. 

If you've just started mountain biking, buy this book now, it'll save you at least two face plants (not guaranteed). Even if you've been biking for a while, provided you're not an expert, it's worth having on your bookshelf.

Update

As much a I like this book Mastering Mountain Bike Skills is better. If I could only choose one, it would be Mastering Mountain Bike Skills. Sorry Chris!