Traditionally, obsessive-compulsive disorder has been classified as an anxiety disorder, but there is increasing evidence that it has schizotypal features - in other words it is a belief disorder. This book describes the ways in which reasoning can be applied to OCD for effective treatment regimes. It moves comprehensively through theoretical, experimental, clinical and treatment aspects of reasoning research, and contains a detailed treatment manual of great value to practitioners, including assessment and treatment protocols and case studies