A telephone survey was conducted of Departments of Corrections in all 50 States, and site visits were completed at 6 programs in 4 States. SI programs may be instituted to deter, rehabilitate, punish, manage offender risk, or reduce prison crowding and cut prison costs. In all States, eligibility for SI is limited to offenders who have not been previously incarcerated; some States limit eligibility to nonviolent offenders, while some require parole or probation eligibility. In some States, SI selection is controlled by judges, while in others it is controlled or strongly influenced by the corrections department. Participation is voluntary in all States. While staff ratios and costs may be the same as or higher or lower than prison costs, savings are substantial because of the reduced time served by inmates. Most programs require strict medical screening, are located in medium security compounds, expel inmates for major misconducts, permit summary punishment, and require physical training and labor. In many programs, inmates are initially subjected to intense verbal confrontation by staff. All programs regulate almost all aspects of inmates' behavior, and obedience to rules is emphasized. All programs also include some form of reentry planning. SI programs last from 3 to 6 months and generally are offered to male inmates. Six programs for females were identified. Inmates report positive feelings about their participation, and probation officers report that SI graduates are more courteous, easier to supervise, and better able to obtain and maintain employment. 1 table.