A no-fly zone, also known as a no-flight zone (NFZ), or air exclusion zone (AEZ), is a territory or area established by a military power over which certain aircraft are not permitted to fly. Such zones are usually set up in an enemy power's territory during a conflict for humanitarian or military reasons without consent of the enemy state, similar in concept to an aerial demilitarized zone, and usually intend to prohibit the enemy's military aircraft from operating in the region. Military action may be employed by the enforcing state and, depending on the terms of the NFZ, may include preemptive attacks to prevent potential violations, reactive force targeted at violating aircraft, or surveillance with no use of force. Air exclusion zones and anti-aircraft defences are sometimes set up in a civilian context, for example to protect sensitive locations, or events such as the 2012 London Olympic Games, against terrorist air attack. A no-fly zone is generally not considered a form of aerial blockade due to its more limited scope compared to an aerial blockade.
No-fly zones are a modern phenomenon established in the 1990s. They can be distinguished from traditional air power missions by their coercive appropriation of another nation's airspace only, to achieve aims on the ground within the target nation. While the Royal Air Force (RAF) conducted prototypical air control operations over various contentious colonies between the two World Wars, no-fly zones did not assume their modern form until the end of the Gulf War in 1991.
