The fourth-generation fighter is a class of jet fighters in service from around 1980 to the present, and represents design concepts of the 1970s. Fourth-generation designs are heavily influenced by lessons learned from the previous generation of combat aircraft. Third-generation fighters were often designed primarily as interceptors, being built around speed and air-to-air missiles. While exceptionally fast in a straight line, many third-generation fighters severely lacked in maneuverability, as doctrine held that traditional dogfighting would be impossible at supersonic speeds. In practice, air-to-air missiles of the time, despite being responsible for the vast majority of air-to-air victories, were relatively unreliable, and combat would quickly become subsonic and close-range. This would leave third-generation fighters vulnerable and ill-equipped, renewing an interest in manoeuvrability for the fourth generation of fighters. Meanwhile, the growing costs of military aircraft in general and the demonstrated success of aircraft such as the McDonnell Douglas F-4 Phantom II gave rise to the popularity of multirole combat aircraft in parallel with the advances marking the so-called fourth generation.

During this period, maneuverability was enhanced by relaxed static stability, made possible by introduction of the fly-by-wire (FBW) flight-control system, which in turn was possible due to advances in digital computers and system-integration techniques. Replacement of analog avionics, required to enable FBW operations, became a fundamental requirement as legacy analog computer systems began to be replaced by digital flight-control systems in the latter half of the 1980s. The further advance of microcomputers in the 1980s and 1990s permitted rapid upgrades to the avionics over the lifetimes of these fighters, incorporating system upgrades such as active electronically scanned array (AESA), digital avionics buses, and infra-red search and track.

Due to the dramatic enhancement of capabilities in these upgraded fighters and in new designs of the 1990s that reflected these new capabilities, they have come to be known as 4.5 generation. This is intended to reflect a class of fighters that are evolutionary upgrades of the fourth generation incorporating integrated avionics suites, advanced weapons efforts to make the (mostly) conventionally designed aircraft nonetheless less easily detectable and trackable as a response to advancing missile and radar technology (see stealth technology). Inherent airframe design features exist and include masking of turbine blades and application of advanced sometimes radar-absorbent materials, but not the distinctive low-observable configurations of the latest aircraft, referred to as fifth-generation fighters or aircraft such as the Lockheed Martin F-22 Raptor.

The United States defines 4.5-generation fighter aircraft as fourth-generation jet fighters that have been upgraded with AESA radar, high-capacity data-link, enhanced avionics, and "the ability to deploy current and reasonably foreseeable advanced armaments". Contemporary examples of 4.5-generation fighters are the Sukhoi Su-30SM/Su-34/Su-35, Shenyang J-15B/J-16, Chengdu J-10C, Mikoyan MiG-35, Eurofighter Typhoon, Dassault Rafale, Saab JAS 39E/F Gripen, Boeing F/A-18E/F Super Hornet, Lockheed Martin F-16E/F/V Block 70/72, McDonnell Douglas F-15E/EX Strike Eagle/Eagle II, HAL Tejas MK1A, CAC/PAC JF-17 Block 3, and Mitsubishi F-2.

Whereas the premier third-generation jet fighters (e.g., the F-4 and MiG-23) were designed as interceptors with only a secondary emphasis on maneuverability, 4th generation aircraft try to reach an equilibrium, with most designs, such as the F-14 and the F-15, being able to execute beyond visual range (BVR) interceptions while remaining highly maneuverable in case the platform and the pilot find themselves in a close range dogfight. While the trade-offs involved in combat aircraft design are again shifting towards BVR engagement, the management of the advancing environment of numerous information flows in the modern battlespace, and low-observability, arguably at the expense of maneuvering ability in close combat, the application of thrust vectoring provides a way to maintain it, especially at low speed.

Key advances contributing to enhanced maneuverability in the fourth generation include high engine thrust, powerful control surfaces, and relaxed static stability (RSS), this last enabled via "fly-by-wire" computer-controlled stability augmentation. Air combat manoeuvring also involves a great deal of energy management to maintain speed and altitude under rapidly changing flight conditions.

Fly-by-wire is a term used to describe the computerized automation of flight control surfaces. Early fourth-generation fighters like the F-15 Eagle and F-14 Tomcat retained electromechanical flight hydraulics. Later fourth-generation fighters would make extensive use of fly-by-wire technology.

The General Dynamics YF-16, eventually developed into the F-16 Fighting Falcon, was the world's first aircraft intentionally designed to be slightly aerodynamically unstable. This technique, called relaxed static stability (RSS), was incorporated to further enhance the aircraft's performance. Most aircraft are designed with positive static stability, which induces an aircraft to return to its original attitude following a disturbance. However, positive static stability, the tendency to remain in its current attitude, opposes the pilot's efforts to maneuver. An aircraft with negative static stability, though, in the absence of control input, will readily deviate from level and controlled flight. An unstable aircraft can therefore be made more maneuverable. Such a 4th generation aircraft requires a computerized FBW flight control system (FLCS) to maintain its desired flight path.