Fifth generation

The current cutting edge of fighter design combines previous emphasis on versatility with new developments such as thrust vectoring, composite materials, supercruise, stealth technology, advanced radar and sensors, and integrated avionics designed to reduce the pilot's workload while vastly improving situational awareness.
Of these, only the American F-22 Raptor, put into production in 2004, is operational, and is often regarded as the first of a new generation of fighters, termed the "fifth-generation". The in-development F-35 Lightning II (formerly Joint Strike Fighter) and the F-22 has influenced the continued development of the fourth-generation designs, and the shape of design work for the Russian PAK FA and other countries' long-term fighter development projects (for instance, the rumoured Chinese Shenyang J-XX project, Indian Medium Combat Aircraft and South Korean KFX). There was some later cancelled technology demonstrators of fifth-generation fighter aircraft. Those include United States YF-23 Black Widow II, Boeing X-32 and McDonnell Douglas X-36 plus Soviet Union Project 1.42, later upgraded by Russia to version 1.44.

Source - http://en.wikipedia.org/wiki/Fighter_aircraft

Generation 4.5 (1990-Present)

This half-generation has been coined to describe the next generation of fighters in service, marked by a stagnation of aerodynamic technologies (compared with the boom of the third-generation) matched with a tremendous advance in avionics and other flight electronics, as a result of applying the advances made in microchip and semiconductor technology in the 1980s and 1990s, as well as limited stealth shaping made possible with supercomputers. A prime example of this generation is the F/A-18E/F Super Hornet, based on the 1970s Hornet design. While the basic aerodynamic features remain the same, the Super Hornet features improved avionics in the form of an all-glass cockpit, a solid-state AESA fixed-array radar, new engines, the structural use of composite materials to reduce weight, and a slightly modified shape to minimize its radar signature. Of these, only the Super Hornet and the Rafale have seen combat action.

Source - http://en.wikipedia.org/wiki/Fighter_aircraft

Fourth generation (1970-1990)

In reaction to the continually rising cost of fighters and the demonstrated success of the F-4 Phantom II, multirole fighters became popular during this period, and even aircraft designed for a specific role (as the F-4 had) acquired multi-role capability. Fighters such as the MiG-23 and Panavia Tornado have versions specially suited for various roles, while true multirole warplanes include the F/A-18 Hornet and Dassault Mirage 2000. This was facilitated by avionics which could switch seamlessly between air and ground modes. As development costs increased, economics further pushed the development for multirole aircraft.
Unlike interceptors of the previous era, most modern air-superiority fighters have been designed to be agile dog-fighters. Fly-by-wire (The U.S. Lockheed Martin F-16 Fighting Falcon was the first fighter to use Fly-by wire, utilizing a token-passing digital control mechanism based on the Texas Instruments TI Falcon Chipset [TMS820/830] - a "Token Ring" network technology developed in conjunction with McDonald Douglas Aircraft - Military Division in St. Louis) controls and relaxed stability is common among modern fighters. Aircraft here make up most of the "fourth generations" of fighter jets.

Source - http://en.wikipedia.org/wiki/Fighter_aircraft

Third generation (1960-1970)

The third generation is marked by maturity in the innovations introduced in the first generation. As this aeronautical development approached maturity, growth in combat capability grew via the introduction of improved missiles, radar, and other avionics. Most significantly, as a result of combat experience with guided missiles, designers conceded that combat could and would degenerate into close dogfights. Guns again became standard, and maneuverability was once again a priority.
These innovations, while greatly improving the capabilities of fighters (the F-4 could carry a payload greater than the B-24 Liberator, a World War II heavy bomber), also came at a considerable increase at cost. Whereas militaries had previously specialized fighters for specific roles, such as night fighter, heavy fighter and strike fighter, in order to counter the growing cost of fighters, militaries began to consolidate missions. The McDonnell F-4 Phantom II was designed as a pure interceptor for the United States Navy, but became a highly successful multi-role aircraft for the Air Force, Navy and Marine Corps as well as many other nations. It is the only combat aircraft to be simultaneously flown by all three American service branches.

Source - http://en.wikipedia.org/wiki/Fighter_aircraft

Second generation (1953-1960)

The second generation describes the integration of many new technologies to greatly improve the fighting capability of the jet fighter. The introduction of guided missiles such as the AIM-9 Sidewinder and AIM-7 Sparrow moved combat to beyond visual range (though it often devolved into dogfights in visual range), necessitating the standardization of radar to acquire targets. Designers experimented with a variety of aeronautical innovations, such as the swept wing, delta wing, variable-geometry wings, and area ruled fuselages. With the aid of swept wing, these were the first production aircraft to break the sound barrier.
The primary specializations of this era were the fighter-bomber (such as the F-105 and the Sukhoi Su-7), and the interceptor (English Electric Lightning and F-104 Starfighter). The interceptor was an outgrowth of the vision that guided missiles would completely replace guns and combat would take place at beyond visual range. As a result, interceptors were designed with a large missile payload and a powerful radar, sacrificing agility in favor of speed and rate of climb.

Source - http://en.wikipedia.org/wiki/Fighter_aircraft

First-generation jet fighters (1944-1953)

First-generation jet fighters (1944-1953)
The first generation represents the first attempts at using turbojets for propulsion, providing greatly increased speed (the efficiency of piston-driven propellers drops off considerably at transsonic speeds). Many of these early jets resembled their piston-driven counterparts in several ways. Many were straight-winged aircraft armed primarily with cannon; radar was not yet in common usage except on specialized night fighters.
The first jets were developed during World War II and saw combat in its last year. Messerschmitt developed the first operational jet fighter, the Me 262. It was considerably faster than piston-driven aircraft, and in the hands of a competent pilot, was practically untouchable. Due to German fuel shortages, however, it saw little use. Nevertheless the plane indicated the obsolescence of piston-driven aircraft. Spurred by reports of the German jets, Britain's Gloster Meteor entered production soon after and the two entered service around the same time in 1944. By the end of the war almost all work on piston powered fighters had ended. Mixed-propulsion designs such as the Ryan FR Fireball saw brief use, but by the end of the 1940s virtually all new combat aircraft were jet-powered.
Despite the advantages, the early jet fighters were far from perfect. Their operational lifespans could be measured primarily in hours; the engines themselves were fragile and bulky, and power could be adjusted only slowly. Innovations such as swept wings, ejector seats, and all-moving tailplanes were introduced in this period.

Source - http://en.wikipedia.org/wiki/Fighter_aircraft

What is a Fighter Aircraft ?

A fighter aircraft is a military aircraft designed primarily for attacking other aircraft, as opposed to a bomber, which is designed to attack ground targets, primarily by dropping bombs. Fighters are comparatively small, fast, and maneuverable. They were developed in response to the fledgling use of aircraft and dirigibles in World War I for reconnaissance and ground attack roles. These early fighters were mostly woodenbiplane with light machin guns As aerial warfare became increasingly important, so did control of the airspace. By World War II, fighters were predominantly metal monoplanes with wing-mounted cannon. Following the war, turbojets replaced piston engines as the means of propulsion, and missiles augmented or replaced guns. For historical purposes, jet fighters are classified by generation. The generation terminology was initiated by Russian defense parlance in referring to the F-35 Lightning II as a "fifth-generation" plane. Years are not exact and intended as a guideline. Modern jet fighters are predominantly powered by one or two turbofan engines, armed primarily with missiles (from as few as two on some lightweight day fighters to as many as eight to ten on air superiority fighters like the Su-27 Flanker or F-15 Eagle), with a cannon as backup armament (typically between 20 and 30mm in calibre), and equipped with a radar as the primary method of target acquisition.

Fighter aircraft are the primary means by which armed forces gain air superiority. At least since World War II, air superiority has been a crucial component of victory in most modern warfare, particularly "conventional" warfare between regular armies, and their acquisition and maintenance represent a very substantial proportion of military budgets in militaries that maintain modern fighter forces.