Her Majesty's Prison Service (HMPS) in England and Wales developed a model accreditation system that has in 3 1/2 years markedly accelerated the effectiveness of correctional treatment programming. Ministers and managers judge the effectiveness of the Prison Service by using key performance indicators (KPIs). Each year the Prison Service agrees to a "contract" with the Home Secretary, and the Home Secretary agrees to give the Prison Service a budget in exchange for operating the Prison Service to certain standards that are defined by targets for each KPI. The contract stands as long as the operating conditions (e.g., the size of the prison population) is within an anticipated range. The head of the Prison Service is responsible for seeing that the targets are met. Nine KPIs are listed and described in this article. A program's having been accredited means that in the view of the General Accreditation Panel (GAP), the program would be likely to reduce reconviction rates if the program was delivered as specified, and this is the leverage created by the system to facilitate and sustain improvement in the Prison Service's treatment programming. This article describes preparation for accreditation, the accreditation criteria, the scoring of the criteria, and evidence for the success of accreditation. Implications of England's and Wales' accreditation program for corrections in the United States are discussed. 50 references and 8 notes