This authoritative book reviews current cognitive-behavioral models of OCD and delineates an innovative, theoretically and empirically grounded approach to assessment and treatment. Leading scientist-practitioner David A. Clark first elaborates and refines existing theories of obsessions and compulsions. He then spells out effective strategies for assessing client needs, developing a clear case formulation, implementing an array of cognitive and behavioral interventions, and troubleshooting potential difficulties. Illustrated with extensive clinical material, the volume is practical and user-friendly. Reproducible appendices feature over a dozen rating scales, client handouts, and homework tasks.