The politicization of imprisonment policy, which began in the 1970's, and the changing age composition of the American population due to the postwar baby boom are important factors. One of the most troublesome aspects of prison populations is the overrepresentation of blacks. This cannot be explained solely or predominantly by racial discrimination in the criminal justice system; the bulk of the differential presence of blacks in prisons appears to result from their differential involvement in those crimes for which prison sentences are often imposed. Three basic approaches exist for relieving prison overcrowding. First, offenders can be diverted from prison to alternatives such as probation. Second, prison sentences can be shortened by a variety of mechanisms such as flow-sensitive sentencing policies and early release provisions. Third, prison capacity can be increased by constructing more facilities. States that are formulating strategies to alleviate prison overcrowding should consider a mixture of these approaches. 6 figures, 5 tables, and 38 references. (Author abstract modified)