预警机（Air Early Warning, AEW）是为了克服雷达受到地球曲度限制的低高度目标搜索距离，同时减轻地形的干扰，将整套雷达系统放置在飞机上，自空中搜索各类空中、海上或者是陆上目标。借由飞行高度，提供较佳的预警与搜索效果，延长容许反应的时间与弹性。空中预警管制机（Airborne Early Warning and Control, AEW&C）除提供早期预警的功能之外，还提供频繁C2BM（指挥和控制，作战管理）功能，类似机场交通管制和其他部队的军事指挥。

空中预警机比较常见的是以客机或者是运输机改装而来，因为这类飞机的内部可使用空间大，能够安装大量电子与维持运作的电力与冷却设备，同时也有空间容纳数字雷达操作人员。也有国家以直升机作为载具，不过这一类的小型空中预警机由于受到载机性能的影响，效果不如以中大型飞机机体改装而来的机种。由于受到军舰空间的限制，除美国E-2空中预警机外，预警直升机多用于海军舰队的早期预警，是目前大多数装备航母国家的重要早期预警手段。

An airborne early warning and control (AEW&C) system is an airborne radar picket system designed to detect aircraft, ships and vehicles at long ranges and perform command and control of the battlespace in an air engagement by directing fighter and attack aircraft strikes. AEW&C units are also used to carry out surveillance, including over ground targets and frequently perform C2BM (command and control, battle management) functions similar to an Air Traffic Controller given military command over other forces. When used at altitude, the radar on the aircraft allows the operators to detect and track targets and distinguish between friendly and hostile aircraft much farther away than a similar ground based radar. Like a ground based radar, it can be detected by opposing forces, but because of its mobility, it is much less vulnerable to counter-attack.