Agile testing is a great book to both new and seasoned test engineers and test managers. At 533 pages, the book might feel a bit heavy but it is actually a pretty light and practical read if you read it to get a solid foundation on agile testing and then as reference. Note that the book is not about test coding techniques.
Part I is an introduction to agile testing and proposes ten principles for agile testers. What I don't know is if there are really 10 principles or if Crispin and Gregory forced it to be that specific number because it sounds better than 9 or 11. In any case, this chapter is a must read for all. Part II discusses organizational challenges, specifically cultural, logistical, and transitional from typical processes. This is a must-read for managers and team leads, and highly advisable for engineers if you want to have a successful test organization fully integrated with an agile organization. I personally encourage the division between development and testing to disappear completely. Part III is about he testing quadrants proposed by Brian Marick (one of the Agile Manifesto signatories) a while back. This is the first time I see the quadrants treated in larger detail and highly recommend it as a must for all.
Part IV is about test automation. It is a good read to understand the advantages of test automation and proposes a test automation strategy. This is a good starting point for test organizations that are new to automation but for mature test automation organizations it might add little value. Test code writing techniques are beyond the scope of this book. Part V illustrates the previous parts and then some by following a tester's activities through an agile iteration and the activities prior to it.
One problem I see way too often in test organizations and the way companies treat their test organizations is due to a lack of understanding not only of the difference between Quality Assurance and testing but also because of the place testing has hi people's minds. This book is a big help to create a cultural shift for the better.