This study consists of three phases. In Phase 1, data from previously conducted pilot studies will be revised and expanded. In Phase 2, the revised data will be used to develop and implement a treatment manual for compulsive hoarding. During this phase, treatment will be flexibly applied to allow for variations in treatment duration and choice of techniques. During Phase 3, participants will be randomly assigned to either CBT or a wait-list control, followed by active treatment for a fixed duration. Therapist adherence and competence will be assessed through audiotaped therapy sessions.