I fully agree with the other reviewers who have given detailed and glowing descriptions of this book and why it is an important work that addresses the real challenges of developing to a relational model in OO environments. Agile techniques are also interwoven into this book, but it is in overcoming the relational-OO challenges that I found this book to be most valuable.
The first part of the book, "Foundational Skills and Knowledge", covers the challenges and how to meet them with eight excellent chapters that truly give the foundational knowledge. The next part, "Evolutionary Database Development", is comprised of seven chapters that introduce Agile techniques as they relate to DB development. Among the two strongest chapters in this part of the book are the ones covering DB refactoring and mapping objects to relational databases. This material, to me, clarified a lot of issues I had before reading this book. Part 3 is more focused on development techniques, with excellent information about concurrency control, access controls and related topics. The final part of the book is specific to general Agile implementation. You need not embrace Agile methods to learn an enormous amount from this book.
If you want to know more about this book's contents you will find a great deal of information on the author's Agile Data web site (paste the ASIN, B0000A3527, into the search box at the top of this page, select All Products and click GO). I also recommend Clifton Nock's "Data Access Patterns: Database Interactions in Object-Oriented Applications" (ISBN 0131401572), which augments this book in many respects.