Compulsive hoarding is a common and often disabling neuropsychiatric disorder. This article reviews the conceptualization, phenomenology, diagnosis, etiology, neurobiology, and treatment of compulsive hoarding. Compulsive hoarding is part of a discrete clinical syndrome that includes difficulty discarding, urges to save, excessive acquisition, indecisiveness, perfectionism, procrastination, disorganization, and avoidance. It was thought to be part of obsessive-compulsive disorder or obsessive-compulsive personality disorder, but recent evidence indicates that it should be classified as a separate disorder with its own diagnostic criteria. Compulsive hoarding is a genetically discrete, strongly heritable phenotype. Neuroimaging and neuropsychological studies are elucidating its neurobiology, implicating dysfunction of ventral and medial prefrontal cortical areas that mediate decision-making, attention, and emotional regulation. Effective treatments include pharmacotherapy and cognitive-behavioral therapy. More research will be required to determine the prevalence, etiology, and pathophysiology of compulsive hoarding and to develop better treatments