The Residential Substance Abuse Treatment (RSAT) for State Prisoners Formula Grant Program encourages States to develop substance abuse treatment programs for incarcerated offenders. This NIJ Special Report summarizes the results of a National Evaluation of RSAT and process evaluations of 12 local sites across the country. Findings include that RSAT has been responsible for substantial increases in the number of residential and nonresidential treatment slots available for offenders with substance abuse problems and the number of staff trained to work in substance abuse treatment programs.