Although all of the programs have a military atmosphere with drill and physical training, along with strict rules and discipline, they differ significantly in decisionmaking, authority, community supervision upon release, program components, and location. Reducing prison crowding is a major goal of all eight programs. This can occur only if program participants would otherwise have gone to prison for terms longer than the prison phase of the shock incarceration program. The programs vary in their ability to achieve this. Those most likely to achieve reductions in prison crowding are those where corrections officials determine which prison-bound offenders will be admitted to the shorter shock incarceration programs. The second major goal of shock incarceration programs is to change offenders through deterrence, rehabilitation, or discipline and respect. The major impact would be a decrease in recidivism. A review of the deterrence literature, however, yields little evidence that such programs will reduce recidivism. This analysis shows the variety of shock incarceration programs that currently exist. Future studies should examine the impact of these programs on prison costs and crowding, as well as how effective they are in changing offenders. 21 tables and 45 references