In my opinion, this is still the core ACT book to read. This book is just packed with a wealth of information, insights, and novel approaches to clinical problems. There is no other ACT book written to date that matches this one in its scope, overview, and coherence in terms of explaining the ACT model and linking it to the basic behavioral principles with underlie the approach. Even though I've had this book for almost a decade, I still refer to it's dogeared and underlined pages almost every week. If you are a therapist interested in ACT, this book should be in your hands.