Interest in acceptance and commitment therapy (ACT) is expanding rapidly. Many of those who are interested in ACT are trained using a mechanistic cognitive behavioural therapy model (or 'MCBT'). Utilizing both ACT and MCBT together can be difficult, because the approaches make different philosophical assumptions and have different theoretical models. The core purpose of this book is to help provide a bridge between ACT and MCBT. The emphasis of this book will be applied psychology, but it will also have important theoretical implications. This book will highlight where ACT and MCBT differ in their predictions, and will suggest directions for future research. It will be grounded in current research and will make clear to the reader what is known and what has yet to be tested.The authors acknowledge that practitioners often have little interest in extended discussions of philosophy and theory. Thus, their discussion of functional contextualism and RFT is grounded clearly in clinical practice. They talk about what functional contextualism means for the practitioner in the room, with a particular client. They describe how RFT can help the practitioner to understand the barriers to effective client action.