Obsessive-Compulsive and Related Disorders (OCRDs) have received considerable attention over the past two decades culminating with the inclusion of a new classification category of "Obsessive-Compulsive and Related Disorders" (OCRDs) in DSM-5. This group of conditions includes OCD along with two newly minted conditions (Hoarding Disorder and Excoriation Disorder) and others previously classified as Somatoform Disorders (Body Dysmorphic Disorder) and Impulse Control Disorders (Hair Pulling Disorder). The implications for research on these conditions, as well as their relations with one another, are significant since their aggregation is based on putative central mechanisms with limited empirical support to date. Indeed, the past decades have seen a dramatic surge in research on OCRDs. Such scholarship has occurred across several domains including clinical phenomenology, assessment, and psychological therapies. A complete synthesis of the emerging data across these domains would be beyond the scope of a single journal article or series of articles while having the ability to comprehensively discuss advances in the field and stimulating in these areasMany of the available textbooks, although meritorious in their own right, are outdated and do not address the most recent research advances and emerging clinical implications. Indeed, the past decade has seen a tremendous growth in knowledge on treatment, assessment, treatment augmentation, and basic science that is not contained fully within existing volumes (see discussion of specific texts further below). Thus, providing a comprehensive textbook that addresses recent advances will provide a much needed update to the field of OCRDs. Furthermore, recent texts primarily address OCRDs from a biological standpoint, neglecting psychosocial theoretical and intervention approaches that enjoy the most empirical support of any conceptual and treatment approaches for most of the relevant conditions. As a result, the literature has been dominated by a single predominant perspective, which does not fully represent the available data or perspectives of front-line clinicians and researchers alike. As researchers and clinicians will be increasingly focused on this topic in light of the changes to DSM-5 - together with the dearth of current objective available information - this book will be a timely addition to the literature in guiding clinicians in advances in OCRDs that will impact their practice. Third, a number of conditions outside the OCRD chapter in DSM-5 are often proposed as "related" to OCD (e.g., misophonia).