Obsessive-compulsive disorder affects approximately one person in 40 and causes great suffering. Effective treatments are available that can help many, and our understanding of the psychology, neurobiology, and clinical treatment of the disorder has advanced dramatically over the past 25 years. Nevertheless, much remains to be learned, and a substantial minority of patients benefit little even from the best treatments we have to offer today. This volume provides the first comprehensive summary of the state of the field, summarizing topics ranging from genetics and neurobiology through cognitive psychology, clinical treatment, related conditions, societal implications, and personal experiences of patients and clinicians. This book is unique in its comprehensive coverage that extends far beyond the realm of cognitive-behavioral therapy. As such it will serve as a valuable introduction to those new to the field, a fascinating resource for OCD suffers and their families, and an essential reference for students, clinicians, and researchers.