The study obtained and reviewed relevant population, cost, and modeling information from the Federal Bureau of Prisons, the National Council on Crime and Delinquency, and corrections agencies in the two States with the largest numbers of inmates (California and Texas). The study also relied on data compiled by the Federal Bureau of Justice Statistics and the U.S. Bureau of the Census, as well as data in private publications. The study found that from 1980 to 1995, the latest year for which complete data were available, the total Federal and State prison population increased at an average annual rate of 8.5 percent. Federal and State corrections agencies, as well as nongovernmental forecasting organizations, have projected that the prison population will continue to increase in future years. Reflecting the growth in inmate populations, U.S. prison (Federal and State) annual operating costs increased from approximately $3.1 billion in fiscal year 1980 to approximately $17.7 billion in current dollars in fiscal year 1994. All prison costs (operating and capital costs) cumulatively totaled approximately $163 billion during the fiscal years 1980 to 1994. To forecast prison inmate populations, the Bureau of Prisons, the National Council on Crime and Delinquency, California, and Texas each use a form of microsimulation modeling. 11 tables and 5 figures, as well as appended supplementary statistics and information