Obsessive-compulsive disorder is considered the fourth most common mental disorder, with a lifetime incidence of 2.5%. Recent research indicates that OCD has content relationships with other mental disorders that can be placed on a dimensional continuum between compulsivity and impulsivity. These so-called spectrum disorders include eating disorders, shopping frenzy, hypochondria, trichotillomania, and self-injurious behavior. In addition to epidemiology, phenomenology, neurobiology, and diagnosis, therapeutic approaches, including drug and psychotherapeutic options, to obsessive-compulsive disorder and the above spectrum disorders are discussed. The book provides hope in the treatment of this serious and long underestimated disease and emphasizes an integrative approach to treatment.