'''Anti-aircraft warfare''' is the counter to [[aerial warfare]]<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=Osprey |year=1973 |page=37}}</ref> and it includes "all measures designed to nullify or reduce the effectiveness of hostile air action" ([[NATO]]'s definition).<ref name="AAP-6">AAP-6</ref> It includes [[Surface-to-air missile|surface based]], subsurface ([[Submarine#Armament|submarine launched]]), and air-based weapon systems, associated sensor systems, command and control arrangements, and passive measures (e.g. [[barrage balloon]]s). It may be used to protect [[naval]], [[army|ground]], and [[air force]]s in any location. However, for most countries, the main effort has tended to be [[homeland defence]]. [[Missile defense|Missile defence]] is an extension of air defence, as are initiatives to adapt air defence to the task of intercepting any projectile in flight.

Most modern anti-aircraft (AA) weapons systems are optimized for short-, medium-, or long-range air defence, although some systems may incorporate multiple weapons (such as both [[autocannons]] and [[surface-to-air missiles]]). ‘Layered air defence’ usually refers to multiple ‘tiers’ of air defence systems which, when combined, an airborne threat must penetrate in order to reach its target; This defence is usually accomplished via the combined use of systems optimized for either short-, medium-, or long-range air defence.

In some countries, such as Britain and Germany during the [[World War II|Second World War]], the [[Soviet Union]], and modern NATO and the United States, ground-based air defence and air defence aircraft have been under integrated command and control. However, while overall air defence may be for homeland defence (including military facilities), forces in the field, wherever they are, provide their own defences against airborne threats.

Until the 1950s, guns firing ballistic munitions ranging from 7.62 mm (.30 in) to 152.4 mm (6 in) were the standard weapons; guided missiles then became dominant, except at the very shortest ranges (as with [[close-in weapon system]]s, which typically use [[rotary cannon|rotary autocannon]]s or, in very modern systems, surface-to-air adaptations of short-range [[air-to-air missile]]s, often combined in one system with rotary cannons).