Agile Testing: A Practical Guide for Testers and Agile Teams by Lisa Crispin and Janet Gregory is an invaluable resource for testers who are or will be making the transition from traditional waterfall testing to testing in a Scrum, XP, or other agile development methodology. This book is comprehensive in its treatment of the subject. It contains a great set of chapters that describe a tester's role through the stages of an agile project, but it is more than a mere blueprint or paint-by-numbers account.
Before they get to that point, they help readers understand common organizational issues that hinder the transition to agile. They elaborate on the implications of the Agile Manifesto to how individuals, teams, and organizations operate. It is not ivory tower wisdom from above either, but it is rather hard fought, experienced based observations that will help novices avoid some of the potential growing pains. In addition, they give a solid taxonomy of test covering functional and non-functional. They address what types of testing to automate and when. Finally, they spend two chapters in detail on automation strategy and implementation. At regular intervals, readers see either "Lisa's Story" or "Janet's Story" that details with the concept being discussed. These either tell what worked well or how they overcame specific challenges.
I found Crispin and Gregory had a very accessible writing style, and they do a great job of getting their point across. If you are a traditional tester who is unsure or even afraid of moving into the agile world, this is the book that you need. They tackle the tough questions that most people have one by one with answers that can be put in practice. I plan to use the wisdom of this book in helping my testing organization make the transition. I highly recommend this book.