PHP in action is mainly focused on object oriented programming with PHP 5. It also covers test-driven development tools, such as unit tests frameworks in PHP as well as several refactoring techniques, applied to PHP. The last part of the book deals with designing web interfaces using templates and how to interact with databases from PHP using objects and SQL. This book is not intended for beginners; the authors assume previous PHP knowledge or at least knowledge of other programming languages. I found the content very relevant to what the book is meant to be covering and some areas on object orientation also apply to any object oriented language, not just PHP. I also liked the way most chapters start with a real world analogy, often with a bit of humor, before jumping into the subject; it was a real pleasure reading this book.