The systems studied included bus, light rail, and heavy rail and represented a variety of sizes and geographical locations. At each site, representatives of both transit organizations and nontransit organizations, such as government agencies and businesses, were interviewed. Security problems discussed included crimes against passengers and employees; crimes involving revenues, including fare evasion by patrons and revenue theft by employees; and crimes against transit property, including vandalism and graffiti. Identified security measures were grouped into three categories: policing activities, security systems and technology, and outreach programs dealing with the public and criminal justice personnel. Transit security was found to be a large and multifaceted problem that seriously detracts from the continued viability of public transportation. Both transit riders and the public bear the financial and social costs of this crime. Better data are needed regarding the problem. Further problems are reactive approaches to transit security, lack of information sharing, and underuse of available security measures. Better recordkeeping, more research, and actions by the Urban Mass Transportation Administration to improve information exchange are needed. Tables, an appendix presenting the study instrument, 34 references, and a bibliography listing 15 sources are supplied.