The escort fighter was a concept for a fighter aircraft designed to escort bombers to and from their targets. An escort fighter needed range long enough to reach the target, loiter over it for the duration of the raid to defend the bombers, and return.

A number of twin-engined heavy fighters with high fuel capacity were designed for escort duties prior to the outbreak of World War II. Such heavy fighters largely failed in their intended escort role during the war, as they were commonly outmaneuvered by more agile single-engined fighters. As the war progressed, longer-range fighter designs and the use of drop tanks allowed single-engined fighters to perform escort duties. In the post-war era the introduction of jet engines and their inherent short range made escort fighters very difficult to build. The related concept of a penetration fighter emerged briefly in the 1950s and again in the 1960s, but did not result in any production aircraft. Parasite fighters—small aircraft designed to be carried by a specialized bomber—were seen as a possible solution to the limited ranges of most traditional escort fighters. First experimented with in WWI, the U.S.-designed XF-85 Goblin would emerge as the last dedicated parasite fighter design and was abandoned in 1949 due to technical issues as well as the advent of practical aerial refueling.

The escort role has been diminished as modern air combat doctrine places a heavy emphasis on the idea of air superiority, and its importance in the ability of an air force to carry out effective operations. Air superiority is defined as a situation in which an air force dominates an airspace to such a degree as to be able to carry out any operations with no interference from enemy air combatants. Fighting an opponent with air superiority in a given battlespace is much harder, as any offensive or defensive tactics are likely to be overwhelmed.

The first major strategic bombing campaigns were carried out during World War I. Initially using Zeppelins, and later by large bomber aircraft such as the Gotha G.IV and Handley Page Type O, these raids were increasingly countered by fighter aircraft. These fighters benefitted substantially from an inherent asymmetry; the attacking aircraft had to fly long distances to reach its target and thus had to be large enough to carry the required fuel load, while the defending fighters were flying only a short distance and therefore were able to be much lighter and have higher performance.

In early 1916, the British War Office drew up a specification for a multi-seat escort fighter intended to protect formations of bombers from German fighters. While the specification did not require high speed, a good field of fire for its guns was essential. Prototype aircraft were built – Armstrong Whitworth F.K.6, Sopwith L.R.T.Tr and Vickers F.B.11 – all three put gunners into nacelles to provide wide fields of fire. The development of effective synchronisation gear which meant smaller fighters could be equally effective led to the end of development of the designs.

As the fighters held the upper hand, raids were almost always carried out at night. During the inter-war era, this led to the creation of dedicated night bomber designs that concentrated on solving the problem of long-range navigation at night. During 1932, in the face of increasingly capable bomber aircraft, the British Prime Minister Stanley Baldwin surmised that interception efforts would inevitably not always succeed and that "the bomber will always get through". Furthermore, due to a lack of precision aiming capabilities, bombers were viewed as likely to attack urban environments in general; Baldwin noted that their primary purpose would be to "kill the enemy's women and children more rapidly than they killed yours".

This state of affairs was considered distasteful and there was some consideration given to methods to allow bombing during the day. Two ideas became popular. The schnellbomber was a very fast aircraft that would simply fly right past the slower fighters due to the extra power of their twin-engine designs. This was demonstrated with great effect at multiple air races during the early 1930s, where light twins easily outperformed fighters. However, this situation only existed for a short period until more powerful aircraft engines emerged in the mid-1930s and once again a single-engine fighter could catch a twin-engine bomber.^{[dubious – discuss]} The other idea was the escort fighter that would attempt to break up attacks by the defense before they could reach the bombers. To have the desired range, the aircraft had to carry a large fuel load, and at the time this demanded a twin-engine aircraft. Such a design would not be able to maneuver with the single-engine day fighters, so attention was given to outright performance.

Luftwaffe strategy was based mostly on daytime tactical bombing and put significant effort into the escort fighter concept before the outbreak of World War II. One of the principal outcomes of this attention was the Messerschmitt Bf 110 heavy fighter, which was widely produced. At the time of its introduction, the Bf 110 had been among the fastest production aircraft ever built, but as had occurred with the schnellbomber designs, by the start of the conflict, its performance lead had been seriously eroded.