His Majesty's Prison Service (HMPS) is a part of HM Prison and Probation Service (formerly the National Offender Management Service), which is the part of His Majesty's Government charged with managing most of the prisons within England and Wales (Scotland and Northern Ireland have their own prison services: the Scottish Prison Service and the Northern Ireland Prison Service, respectively).

The Director General of HMPS, currently Phil Copple, is the administrator of the prison service. The Director General reports to the Secretary of State for Justice and also works closely with the Prisons Minister, a junior ministerial post within the Ministry of Justice.

The statement of purpose for His Majesty's Prison Service states that "[His] Majesty's Prison Service serves the public by keeping in custody those committed by the courts. Our duty is to look after them with humanity and help them lead law abiding and useful lives in custody and after release". The Ministry of Justice's objective for prisons seeks "Effective execution of the sentences of the courts so as to reduce re-offending and protect the public".

It has its head office in Clive House in London, and previously its head office was in Cleland House in the City of Westminster, London.

The British Overseas Territory of Bermuda's HM Prison Service (renamed the Department of Corrections in 2002) is a separate organisation.