United Nations (UN) rules concerning the treatment of inmates in correctional institutions, especially libraries, are detailed. The article reports on the findings of a UN survey concerning the implementation of these rules. Prison library services are seen to reflect the goals of correctional institutions (e.g., rehabilitation, confinement, punishment, and deterrence). These aims and philosophies affect the size and makeup of the collection of books and other materials, the types of services made available, and access to the library itself. Library services to correctional institutions are discussed in terms of the influence of the public library system and the organization patterns; the effectiveness of the programs of library service; the scope of library collections; library services programs for young offenders; the variety of programs, books per capita, and staffing; and problems such as outdated book collections, lack of qualified staff, and inadequate physical facilities. Other library services discussed include encouraging trends in the provision of library services to correctional facilities and the usefulness of library service in the rehabilitation process. Examples of library services are given in countries throughout the world. A list of 73 references is appended.