The Happiness Trap

An excellent book on Acceptance and Commitment Therapy (ACT). Harris breaks down complex ideas into easy to understand plain English, and I would recommend this book to anyone. The start and end are phenomenal, the middle pretty good. Although it's very easy to read, you will definitely take your time due to the subtle complexity of the text. Make sure you complete his exercises, even when you don't feel like it, they're absolutely worth it to getting the most out of the book.