More than 1.9 million American adults were in Federal prisons, State prisons, and local jails at midyear 1999. More than half of these prisoners said they had used drugs in the month before their offense, 16 percent said they had committed their offense to get money for drugs, and two-thirds were actively involved with drugs prior to their incarceration. The article claims that these statistics could change if inmates with substance abuse problems were treated. In light of these statistics, Congress passed the Violent Crime Control and Law Enforcement Act of 1994, which directs the Department of Justice to support States in their efforts to provide treatment to offenders by making funds available for the Residential Substance Abuse Treatment (RSAT) for State Prisoners Formula Grant Program. The RSAT initiative uses therapeutic community, cognitive skills/behavior, and a 12-step abstinence and support process used by groups such as Alcoholics Anonymous. Preliminary indications are that the RSAT initiative has helped States increase their substance abuse treatment capacity within correctional facilities. In addition, development of screening and assessment tools that identify inmates suitable for the program has resulted in better use of correctional resources. The article contains data on RSAT evaluation reports from 11 states and one national evaluation. Notes