Like most human behaviors, saving and collecting possessions can range from totally normal and adaptive to excessive or pathological. Hoarding, or compulsive hoarding, are some of the more commonly used terms to refer to this excessive form of collectionism. Hoarding is highly prevalent and, when severe, it is associated with substantial functional disability and represents a great burden for the sufferers, their families, and society in general. It is generally considered difficult to treat. Hoarding can occur in the context of a variety of neurological and psychiatric conditions. Although it has frequently been considered a symptom (or symptom dimension) of obsessive-compulsive disorder, and is listed as one of the diagnostic criteria for obsessive-compulsive personality disorder, its diagnostic boundaries are still a matter of debate. Recent data suggest that compulsive hoarding can also be a standalone problem. Growing evidence from epidemiological, phenomenological, neurobiological, and treatment studies suggests that compulsive hoarding may be best classified as a discrete disorder with its own diagnostic criteria.