The Sukhoi Su-35 (Russian: Сухой Су-35; NATO reporting name: Flanker-E/M, occasionally nicknamed "Super Flanker") is the designation for two improved derivatives of the Su-27 air-defence fighter. They are single-seat, twin-engine, supermaneuverable, 4.5 generation air superiority fighters, designed by the Sukhoi Design Bureau and built by Sukhoi.

The type was originally developed by the Soviet Union from the Su-27 and was known as the Su-27M. It incorporated canards and a multi-function radar giving it multi-role capabilities. The first prototype made its maiden flight in June 1988. Following the dissolution of the Soviet Union, Sukhoi relabeled it Su-35 in hopes of attracting export orders. Fourteen aircraft were produced and used for tests and demonstrations; one example had thrust-vectoring engines and was in turn redesignated the Su-37. A sole Su-35UB two-seat trainer was also built in the late 1990s that resembled the Su-30MK family.

In 2003, Sukhoi embarked on a second "deep" modernization of the Su-27 to serve as an interim export aircraft awaiting the development of the Sukhoi PAK FA (Su-57) program. Also known as the Su-35, this version incorporates technology from the PAK FA program and has a redesigned cockpit and weapons-control system and features thrust-vectoring engines in place of the canards. The type made its first flight in February 2008. Although it was designed for export, the Russian Air Force became the launch customer in 2009, with the production version designated Su-35S. China's People's Liberation Army Air Force has also placed orders.

The first aircraft design to receive the Su-35 designation had its origins in the early 1980s, at a time when the Su-27 was being introduced into service with the Soviet Armed Forces. The definitive production version of the Su-27, which had the factory code of T-10S, started mass ("serial") production with the Komsomolsk-on-Amur Aircraft Production Association (KnAAPO) in 1983. The following year, this Su-27 version reached initial operational readiness with the Soviet Air Defence Forces. Having begun work on an upgraded Su-27 variant in 1982, the Sukhoi Design Bureau was instructed in December 1983 by the Soviet Council of Ministers to use the Su-27 as the basis for the development of the Su-27M (T-10M). Nikolay Nikitin would lead the design effort throughout much of the project's existence, under the oversight of General Director Mikhail Simonov, who had been the chief designer of the Su-27 along with Mikhail Pogosyan.^{[citation needed]}

While sharing broadly the blended wing-body design of the Su-27, the Su-27M is visibly distinguished from the basic version by the addition of canards, which are small lifting surfaces, ahead of the wings. First tested in 1985 using an experimental aircraft, the canards, in complement with the reshaped wing leading-edge extension, redirected the airflow in such a way so as to eliminate buffeting at high angles of attack and allowed the airframe to sustain 10-g manoeuvres (as opposed to 9 g on the Su-27) without additional structural reinforcement. More importantly, when working with the relaxed-stability design and the accompanying fly-by-wire flight-control system, the aerodynamic layout improved the aircraft's manoeuvrability and enabled it to briefly fly with its nose past the vertical while maintaining forward momentum. Because of this, theoretically, during combat the pilot could pitch the Su-27M up 120 degrees in under two seconds and fire missiles at the target. Other notable visible changes compared to the T-10S design included taller vertical tails, provisions for in-flight refuelling and the use of two-wheel nose undercarriage to support the heavier airframe.

Besides the increase in manoeuvrability, another feature that distinguished the Su-27M from the original design was the new weapons-control system. The centrepiece of this system was the multi-function N011 Bars (literally "Leopard") phased-array radar with pulse-Doppler tracking that allowed it to detect targets below the horizon. First installed on the third prototype, the radar transformed the Su-27M from simply being an air-defence fighter into a multi-role aircraft capable of attacking ground targets. Compared to the N001 Myech ("Sword") radar of the Su-27, which could track 10 targets and only direct two missiles towards one target at a time, the new radar could track fifteen targets and direct missiles towards six of them simultaneously. The extra weight of the N011 radar at the front of the aircraft necessitated the addition of the canards; engineers would only later discover the aerodynamic advantages of these devices. In addition, an N012 self-defence radar was housed in the rearward-projecting tail boom, making the aircraft the first in the world to have such a radar. Other changes to the aircraft included the use of uprated turbofan engines, as well as the increased use of lightweight composites and aluminium-lithium alloys in the aircraft's structure.

In 1987, Sukhoi started converting the first prototype (designated T10M-1) from a T-10S airframe at its experimental plant in Moscow. Although it had canards, the first prototype, like several subsequent aircraft, lacked the many physical alterations of the new design. It made its first flight after conversion on 28 June 1988, piloted by Oleg Tsoi, followed by the second prototype in January 1989. Following the conversions of the two Su-27M prototypes, the actual production of the aircraft was transferred to the country's Far East where it was carried out by KnAAPO. The third aircraft (T10M-3), which was the first new-built Su-27M and first to be constructed by KnAAPO, made its first flight in April 1992. By then, the Soviet Union had disintegrated, and the ensuing economic crisis in Russia throughout the 1990s meant that the original plan to mass-produce the aircraft between 1996 and 2005 was abandoned, with the aircraft to serve as experimental test-beds to validate the canards, the flight-control system and thrust-vectoring technology. In total, two prototypes, nine flying pre-production and three production aircraft were constructed by 1995; the production aircraft were delivered in 1996 to the Russian Air Force for weapons testing.

By the time of the disintegration of the Soviet Union, Sukhoi had been demonstrating the Su-27M to senior defence and government officials. With its debut to a Western audience at the 1992 Farnborough Airshow, the company redesignated the aircraft as Su-35. The aircraft subsequently made flying demonstrations overseas in an effort to attract export orders, starting in November 1993 with Dubai, where Viktor Pugachev flew it in a mock aerial engagement with an Su-30MK in front of spectators. The aircraft then flew in Berlin and Paris, and would be a regular feature at Moscow's MAKS Air Show. The Russian government cleared the aircraft for export during Sukhoi's unsuccessful sales campaign in South Korea during the late 1990s and early 2000s; the company also marketed the aircraft to Brazil, China and the United Arab Emirates.