Missile defence is a system involved in the detection, tracking, interception and destruction of attacking missiles.

Originally conceived as a defence against nuclear-armed intercontinental ballistic missiles, its application has broadened to include shorter-ranged non-nuclear tactical and theatre missiles.

As of 2012, there is no pressing need for an American missile defence system. Those countries that do have nuclear armed missiles that can reach the United States are all either American allies, or are in the case of Russia and China, in a stable deterrence posture with the United States.