This article analyzes the supply and demand sides in nuclear smuggling, as well as intermediaries between them, based on the 700 illicit trafficking incidents collected by the Stanford Database on Nuclear Smuggling, Theft, and Orphan Radiation Sources (DSTO) for the period 1991 to 2002. The supply side consists of people with access to nuclear and other radioactive material. It can be subdivided into civilian employees at source facilities, ranging from technicians to top managers; military personnel; and security guards. Intermediaries--traffickers and middlemen--can be categorized as amateurs, opportunist businessmen and firms, and organized crime groups. The demand side is represented by proliferating nation states, terrorist organizations, religious sects, separatist movements, and criminal groups or individuals interested in using nuclear and other radioactive material for malevolent purposes, such as murder, deliberate exposure, blackmail, and extortion.