Agile Testing takes a look at quality from nearly every angle there is, and not just from the tester's perspective. It is not a nitty-gritty how-to test software -- it is assumed that if you are a tester you already have experience with this. It is comprehensive, starting with a 30,000 foot overview of agile and the different types of testing in an agile project, and then proceeding to cover various aspects of producing quality software, mostly from the point of view of testers. Testers are seen as a core part of the development team, and quality is seen as everyone's responsibility.
The book covers many different types of testing, both in terms of how tests are performed (manual vs automated, scripted vs exploratory), or for different purposes (testing correctness vs robustness, ferreting out bugs, solving the right problem, and solving the problem right), or to test different layers of an application (functionality, scalability, usability, performance, load, security). There is an excellent deep dive into automation -- both in terms of how-to automate, and what to automate. The book goes beyond just the mechanics of testing, covering people issues, process issues, and tool issues.
Highly recommended for anyone who works on an agile team, who would like to work on an agile team, or who would like to help transition their team to more agile processes.
subject: Agile Testing: A Practical Guide for Testers and Agile Teams