The first prison psychologists in Great Britain was appointed in 1946. Since then, the service has grown to include 84 full-time psychologists, 2 part-time psychologists, and 30 testers. The service's overall mission is to carry out research for the purpose of assisting in the management and planning for the prison system. The service was originally intended to perform prisoner evaluation, and two-thirds of the prison psychologists are still involved in assessment work. Generally the role of this group is shifting, however, to one of social engineering. The development of the prison psychology service has occurred during a period when the criminal justice trend has been to reduce the rate of imprisonment for certain categories of offenses and to provide longer sentences for those still being sent to prison. Psychologists are currently primarily involved in behavioralistic therapy work as well as in management activities. The psychologists primary contribution to social engineering in the prisons, thus, is one of providing research data through which system management problems, especially those related to internal security, can be conceptualized and attacked. Psychologists are being directly recruited into the management program of the state, with the resulting development of statistical data production and behavioral design as regulative principles of the state prison system. Thirty references are provided.