Air Raid Precautions (ARP) refers to a number of organisations and guidelines in the United Kingdom dedicated to the protection of civilians from the danger of air raids. Government consideration for air raid precautions increased in the 1920s and 30s, with the Raid Wardens' Service set up in 1937 to report on bombing incidents. Every local council was responsible for organising ARP wardens, messengers, ambulance drivers, rescue parties, and liaison with police and fire brigades.

From 1 September 1939, ARP wardens enforced the "blackout". Heavy curtains and shutters were required on all private residences, commercial premises, and factories to prevent light escaping and so making them a possible marker for enemy bombers to locate their targets.

With increased enemy bombing during the Blitz, the ARP services were central in reporting and dealing with bombing incidents. They managed the air raid sirens and ensured people were directed to shelters. Women were involved in ARP services through the Women's Voluntary Service.

The Auxiliary Fire Service was set up in 1938 to support existing local fire services, which were amalgamated into a National Fire Service in 1941.

From 1941 the ARP officially changed its title to Civil Defence Service to reflect the wider range of roles it then encompassed. During the war almost 7,000 Civil Defence workers were killed. In all some 1.5 million men and women served within the organisation during World War Two. Over 127,000 full-time personnel were involved at the height of the Blitz but by the end of 1943 this had dropped to 70,000. The Civil Defence Service was stood down towards the end of the war in Europe on 2 May 1945.

Between 1949 and 1968 many of the duties of the Civil Defence Service were resurrected through the Civil Defence Corps.