Obsessive-compulsive disorder (OCD) is a complex set of thoughts and behaviors that can vary greatly from person to person and can be related to and complicated by a wide range of other disorders. Clinicians are confronted with the challenge of accurately classifying its many variants and developing effective, systematic treatments for them. Some believe that OCD and related problems should be treated as subtypes of one condition; others argue that OCD is composed of a spectrum of many similar conditions that should be treated individually. In this handbook, Jonathan S. Abramowitz, Dean McKay, and Steven Taylor present an approach to diagnosis and treatment that considers subtype and spectrum concepts. They examine specific presentations of OCD—the symptoms—that are often seen in practice as well as the many disorders that may fall within the OCD spectrum. For each symptom and putative spectrum condition, they discuss empirical support, theories of etiology, and treatment issues. The volume covers cognitive-behavioral and biological factors, as well as the latest approaches to psychological and pharmacologic therapy, including complicating factors in treatment. In concluding chapters, the authors critically address the current literature on proposed subtype and spectrum disorders, consider the clinical implications of the literature, and map out a comprehensive, integrated approach for understanding OCD and related conditions. The only work on OCD that covers treatment options for specific symptoms and the full spectrum of related disorders, this handbook is a must-have for clinicians who are dedicated to improving the lives of patients with these challenging mental conditions.