空军是现代化三军当中成立最晚的一支，许多国家直到第一次世界大战结束之后才有独立的空军出现。空军的任务在于利用飞机与其他在空中飞行的武器系统进行武力投射，保护我方空域的充分使用，压制作战另外一方对于我方空域的干扰与使用他们自己的空域，支持其他军种达到战术与战略目标的运行。

许多国家的编制上，空军必须支持陆军作战的需求，包括对地面目标的攻击，空运，空投以及其他相关的任务。即使这些国家的陆军拥有自己的飞机，通常在任务或者是飞机的型态上与空军是有所区别。有些国家的空军同时也指挥弹道飞弹与防空飞弹兵力与系统。也有的国家在空军的编制内有进行陆上作战的特种部队或者是空降部队。

For military aviation conducted by armies and navies, see army aviation and naval aviation.

An air force, also known in some countries as an air army, is in the broadest sense, the national military organization that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an army, navy, or a marine corps. Typically, air forces are responsible for gaining control of the air, carrying out strategic and tactical bombing missions, and providing support to land and naval forces.