This handbook examines evidence-based treatment of obsessive-compulsive and related disorders for a broad clinical audience. Focusing on both children and adults with these conditions, it discusses various manifestations of OCD (e.g., contamination, perfectionism), related conditions (e.g., hoarding, trichotillomania, and Tourette syndrome), and cases with complicating factors. Chapters describe case specifics, offer assessment guidelines, and illustrate evidence-based psychotherapy. Case examples depict real-life complexities of presentation, notably in terms of comorbid conditions and hard-to-treat subpopulations. Topical areas addressed in the Handbook include:Phenomenology, assessment, and treatment of multiple types of OCD in adults and children. Treating "not just right experiences" in children with OCD. Treating obsessive compulsive disorder in very young children. Treatment of OCD comorbid with other disorders like depression and Autism Spectrum Disorder. Treatment of OCD when presenting with complicating factors like limited insight, extreme family accommodation, and poor motivation. The Clinical Handbook of Obsessive-Compulsive and Related Disorders is an essential resource for clinicians and professionals as well as researchers, and graduate students in clinical psychology, psychiatry, social work, counseling programs, pediatrics, public health, and related disciplines.