The Special Air Service (SAS) is a special forces unit of the British Army. The SAS was founded in 1941 as a regiment, and later reconstituted as a corps in 1950. The unit undertakes a number of roles including covert reconnaissance, counter-terrorism, direct action and hostage rescue. Much of the information and actions regarding the SAS is highly classified, and is not commented on by the British government or the Ministry of Defence due to the sensitivity of their operations.

The corps currently consists of the 22nd Special Air Service Regiment, the regular component under operational command of United Kingdom Special Forces, as well as the 21st (Artists) Special Air Service Regiment (Reserve) and the 23rd Special Air Service Regiment (Reserve), which are reserve units under operational command of the 1st Intelligence, Surveillance and Reconnaissance Brigade.

The Special Air Service traces its origins to 1941 and the Second World War. It was reformed as part of the Territorial Army in 1947, named the 21st Special Air Service Regiment (Artists Rifles). The 22nd Special Air Service Regiment, which is part of the regular army,