This article describes the Policy and Service Characteristics Inventory (PASCI), which assesses the policies and services of hospital and community-based substance abuse and psychiatric residential programs for adults. Developed using data from 96 representative programs, the PASCI has nine dimensions that have good internal consistency, are relatively independent, and are quite stable. In comparison to psychiatric programs (N = 43), substance abuse programs (N = 53) had more restrictive admissions policies and were less tolerant of problematic resident behavior; provided less individual choice and privacy, but more formal structures for resident control and policy clarity; and offered less daily living assistance. Compared to community-based substance abuse programs, hospital-based programs had less restrictive admissions policies, provided residents with less choice and control but more policy clarity, and offered more health and treatment and social-recreational services. The PASCI dimensions were related to substance abuse programs' organizational features such as size and staffing, and to program-level outcomes such as the proportion of patients who successfully complete the program. Potential applications of the PASCI and the full inventory of which it is a part are discussed.