A fighter aircraft is a military aircraft designed primarily for air-to-air combat against other aircraft, as opposed to bombers and attack aircraft, whose main mission is to attack ground targets. The hallmarks of a fighter are its speed, maneuverability, and small size relative to other combat aircraft.

Many fighters have secondary ground-attack capabilities, and some are designed as dual-purpose fighter-bombers. Often, aircraft that do not fulfill the standard definition are called fighters. This may be for political or national security reasons, or for advertising purposes or other reasons.

A fighter's main purpose is to establish air superiority over a battlefield. Since World War I, achieving and maintaining air superiority has been essential for victory in conventional warfare. The success or failure of a belligerent's efforts to gain air supremacy hinges on several factors including the skill of its pilots, the tactical soundness of its doctrine for deploying its fighters, and the numbers and performance of those fighters. Because of the importance of air superiority, since the dawn of aerial combat armed forces have constantly competed to develop technologically superior fighters and to deploy these fighters in greater numbers, and fielding a viable fighter fleet consumes a substantial proportion of the defense budgets of modern armed forces.