The book is a definitive guide to the act of yarn bombing. It is chock full of examples, photos, and patterns, and offers plenty of information on the history of yarn bombing, and on the individuals and groups who initiated it, including those who continue to tag.
In addition to yarn graffiti, and how to be successful with it, there is also plenty of general reference on how to start knitting and crocheting, and offers instructions and resources to get you going with needle arts. I find the idea of craft and street art intertwining truly fascinating. If you're evenly slight intrigued, check out this book!
http://www.yarnbombing.com is the authors' blog with LOTS of photographic evidence.