Crime rates are likely to decline in the future as the age distribution of the population shifts. Thus, the prison population should decline by about 1990. The current large prison populations have resulted from demographic factors and from an increase in punitiveness in our society. The five possible strategies for dealing with the current overcrowding are doing nothing, constructing additional capacity, using selective incapacitation, diverting offenders into alternative treatment or shortening the time served, and basing sentencing and release policies on current populations. A reasonable strategy would be to use a mixed approach. An appropriate short-term strategy might be the 'safety valve' policy adopted by Michigan in 1981. Under that approach, a corrections commission monitors the prison populations and reports to the governor, who may reduce minimum sentences by up to 90 days when the prison populations exceed their capacity for more than 30 days. For the next decade, many States may need to provide temporary extra capacity by converting vacated State mental hospitals or other such State residential facilities. States should also establish sentencing commissions to set sentencing guidelines. Meanwhile, research should focus on improving the selection process in sentencing and on the overall prison planning process.