GCHQ works in partnership with the Security Service and the Secret Intelligence Service to protect the UK's national security interests GCHQ is one of the three UK Intelligence Agencies and a part of the UK's National Intelligence Machinery GCHQ's headquarters are in Cheltenham CESG is the Information Assurance arm of GCHQ and is the Government's National Technical Authority for IA responsible for enabling secure and trusted knowledge sharing, which helps its customers achieve their aims Our primary customers are the Ministry of Defence, the Foreign and Commonwealth Office and law enforcement agencies but we also serve a wide range of other Government Departments