The study obtained data from a literature search; a survey of the 50 State prison systems, the District of Columbia, and the Federal Bureau of Prisons; structured onsite interviews in 9 jurisdictions; and document analysis. Data on the extent of prison gangs encompass the aggregate number of prison gangs in the Nation, the number of gangs in each State, and the number of gang members. A review of the history of prison gangs in the United States traces their beginning to Washington State in 1950 and then describes their development in other regions and States. A discussion of the nature of prison gangs focuses on their general structure and operation, including initiation requirements, leadership characteristics, gang member relationships with nongang inmates, and gang activities within prisons. Some prison gang problems identified are drug trafficking, intimidation of nongang inmates, strong-arm extortion, violence, conflicts between gangs, and contracted inmate murders. The study found that no prison system methodically identifies, tracks, and maintains ongoing intelligence on prison gangs. Data also indicate the frequency with which corrections systems use each of 13 identified strategies for countering prison gangs and their activities. Major recommendations include (1) the development of a policy position on prison gangs and procedures for detecting early signs of gang activity, (2) the construction of smaller prison facilities, (3) the establishment of prison gang task forces, and (4) a systematic debriefing of former gang members to obtain useful information. The report also recommends that prison systems share with one another models of gang control that have and have not worked in their jurisdictions. Appendixes contain extensive information and tabular data. A 48-item bibliography is included.