This guide is designed to assist all libraries, including school, public, academic, and specialized libraries such as prison and institutional libraries, to better serve the needs of people of all ages who are mentally retarded. An overview provides a definition of mental retardation, places services for people with mental retardation in historical context, and outlines current trends. The body of the document consists of guidelines covering three important areas: service needs of people with mental retardation (functional disabilities and access to programs and services), the need for information about mental retardation (service outcomes for individuals and service providers established by the Accreditation Council on Services for People with Disabilities, and performance measures for library services for people with mental retardation), and the service outcomes for those providing services to people with mental retardation. (AEF)