The Sukhoi Su-27 (Russian: Сухой Су-27) (NATO reporting name: Flanker) is a twin-engine supermaneuverable fighter aircraft designed by Sukhoi. It was intended as a direct competitor for the large United States fourth-generation fighters such as the Grumman F-14 Tomcat and F-15 Eagle, with 3,530-kilometre (1,910 nmi) range, heavyaircraft ordnance, sophisticated avionics and high maneuverability. The Su-27 was designed for air superiority missions, and subsequent variants are able to perform almost allaerial warfare operations. It was designed with the Mikoyan MiG-29 as its complement (The role of the Fulcrum is tactical air superiority over the battlefield, engaging NATO fighters and strike aircraft).

The Su-27 entered service with the Soviet Air Forces in 1985. The primary role was long range air defence against American SAC B-1B and B-52G/H bombers, protecting the Soviet coast from aircraft carriers and flying long range fighter escort for Soviet heavy bombers such as the Tu-95 "Bear", Tu-22M "Backfire" and Tu-160 "Blackjack".

There are several related developments of the Su-27 design. The Su-30 is a two-seat, dual-role fighter for all-weather, air-to-air and air-to-surface deep interdiction missions. The Su-33 'Flanker-D' is a naval fleet defense interceptor for use on aircraft carriers. Further versions include the side-by-side two-seat Su-34 'Fullback' strike/fighter-bomber variant, and the Su-35 'Flanker-E' improved air superiority and multi-role fighter. The Shenyang J-11 is a Chinese licence-built version of the Su-27.