This paper describes the development of a taxonomy of residential facilities for mentally retarded people based on program model, size, and operation. Data are presented on the use of the classification system in a national survey of 15,633 residential facilities for mentally retarded persons in the United States. Program models are defined (supported natural home, foster home, group residence, semi-independent living facility, supported independent living, board and supervision facility, personal care home, and specialized nursing facility) and national summary data are provided. Classificatory problems are discussed (primarily confusion over distinctions among boarding and supervision facilities, foster homes, and personal care homes) and suggested refinements to the taxonomy are presented. (Author/CL)