Obsessive compulsive disorder (OCD) has perplexed clinicians and researchers for many years. Despite recent advances in our understanding of and ability to treat this debilitating problem, many people with OCD do not benefit or benefit only marginally from existing treatments. Newer approaches and a better understanding of the pathogenesis of OCD are needed. One such approach that has shown considerable promise in recent years is cognitive therapy. Recent studies have found cognitive therapy to be an effective treatment for OCD, and research on cognitive theory for OCD is rapidly expanding. This volume assembles nearly all of the major investigators responsible for the development of cognitive therapy (and theory) for OCD, as well as other major researchers in the field to write about cognitive phenomenology, assessment, treatment, and theory related to OCD. Each chapter of the book is written by an expert in the area. The first section of the book describes the domains of cognition in OCD and the subsequent section outlines measurement strategies where the efforts of an international working group of scholars to develop measures of OCD cognition are described. Reviews of OCD cognitions in OCD spectrum disorders and in specific populations (for example, the elderly and children) are reviewed in following sections. Finally, the role of these cognitions and cognitive processes in treatment is described.