The process evaluation of the Residential Substance Abuse Treatment (RSAT) program of the Georgia Department of Corrections (GDC), federally funded and conducted by the Wellsys Corporation, examined the RSAT program in sufficient detail so that the GDC had the information necessary to assess the program’s quality, efficiency, and effectiveness and provided needed contextual framework for an outcome evaluation of the program. There are 7 RSAT programs operating at 4 prisons in the GDC system (Scott, Macon, Calhoun, and Pulaski) with a total of 310 beds available for program participants. The methods and data sources utilized included interviews with GDC and Spectrum Health Services/CiviGenics (an independent vendor of health services operating in the GDC and administering the RSAT program) staff, examination of computerized databases, observation at service delivery sites, and examination of a variety of written materials and research. The findings suggested that the RSAT program was operating in a way reflective of its design and the intent of its designers. The program’s actual structure, setting, and content conformed to what was originally proposed. Program benefits showed lower rates of institutional misconduct and significant attitudinal and behavioral change as participants progressed through the program. Weaknesses focused on the selection and referral processes and the lack of sufficient aftercare services upon graduation and release from prison. There was a lack of communication between various entities within the GDC and a lack of knowledge concerning the RSAT program among diagnostic and classification staff. Specific program recommendations included: (1) address deficiencies with the MIS system allowing more complete and comprehensive data collection, retrieval and reporting features; (2) implement a standardized system of identifying inmates’ degree of substance use and involvement; (3) refine and simplify the referral process; (4) address and resolve issues between various GDC units and the parole authorities; and (5) substantially increase the opportunities available for aftercare upon release. Appendices