The second edition of The Oxford Handbook of Obsessive-Compulsive and Related Disorders focuses on the obsessive-compulsive and related disorders (OCRDs), newly described in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM). The OCRDs include obsessive-compulsive disorder (OCD), body dysmorphic disorder, hoarding disorder, trichotillomania (hair-pulling disorder), and excoriation (skin-picking) disorder. In the handbook, leading experts review current evidence on the phenomenology, epidemiology, assessment, and treatment of the OCRDs, as well as the presentation of the conditions in special populations. The introductory chapter provides a brief history of OCD, an account of its role in the DSM, and an overview of the chapters to follow.