Close air support (often abreviated "CAS") is the use of military aircraft in a ground attack role against targets in close proximity to one's own troops, in support of ground combat operations. In this role, aircraft serve a purpose similar to that of artillery. Close air support is a part of the modern combined arms doctrine. It should be noted that military aircraft can also provide air support in the ground attack role by attacking targets that are not in close proximity to one's own troops; such attacks deeper in the enemy's rear are nowadays referred to as air interdiction.

The Luftwaffe were early pioneers of close air support, integrating it heavily into the doctrine of blitzkrieg used in World War II. Artillery was slow and required time to set up a firing position. Aircraft were better able keep up with the fast advances of the German panzer columns. The aircraft used most famously in this role was the Ju 87 Stuka, famous as much for its psychological effect as for its direct military capabilities.

Close air support was also important in World War II amphibious operations, where aircraft carriers could provide support for soldiers landing on the beaches.

In the Vietnam War, the United States introduced fixed-wing gunships, cargo aircraft modified as gun platforms to serve as close air support and air interdiction aircraft. The first was the AC-47 Spooky. Later models include the AC-119 and the AC-130.