The Airbus A340 is a long-range, wide-body passenger airliner that was developed and produced by Airbus. In the mid-1970s, Airbus conceived several derivatives of the A300, its first airliner, and developed the A340 quadjet in parallel with the A330 twinjet. In June 1987, Airbus launched both designs with their first orders, and the A340-300 took its maiden flight on 25 October 1991. It was certified along with the A340-200 on 22 December 1992 and both versions entered service in March 1993 with launch customers Lufthansa and Air France. The larger A340-500/600 were launched on 8 December 1997; the A340-600 flew for the first time on 23 April 2001 and entered service on 1 August 2002.

Keeping the eight-abreast economy cross-section of the A300, the early A340-200/300 has a similar airframe to the A330-200/300. Differences include four 151 kN (34,000 lbf) CFM56s instead of two high-thrust turbofans to bypass ETOPS restrictions on trans-oceanic routes, and a three-leg main landing gear instead of two for a heavier 276 t (608,000 lb) Maximum Takeoff Weight (MTOW). Both airliners have fly-by-wire controls, which was first introduced on the A320, as well as a similar glass cockpit. The A340-500/600 are longer, have a larger wing, and are powered by 275 kN (62,000 lbf) Rolls-Royce Trent 500 for a heavier 380 t (840,000 lb) MTOW.

The shortest A340-200 measured 59.4 m (194 ft 11 in), and had a 15,000-kilometre (8,100-nautical-mile) range with 210–250 seats in a three-class configuration. The most common A340-300 reached 63.7 m (209 ft 0 in) to accommodate 250–290 passengers and could cover 13,500 km (7,300 nmi). The A340-500 was 67.9 m (222 ft 9 in) long to seat 270–310 over 16,670 km (9,000 nmi), the longest-range airliner at the time. The longest A340-600 was stretched to 75.4 m (247 ft 5 in), then the longest airliner, to accommodate 320–370 passengers over 14,450 km (7,800 nmi).

As improving engine reliability allowed ETOPS operations for almost all routes, more economical twinjets replaced quadjets on many routes. On 10 November 2011, Airbus announced that the production reached its end, after 380 orders had been placed and 377 delivered from Toulouse, France. The A350 is its successor; the McDonnell Douglas MD-11 and the Boeing 777 were its main competitors. By the end of 2021, the global A340 fleet had completed more than 2.5 million flights over 20 million block hours and carried over 600 million passengers with no fatalities. As of March 2023^[update], there were 203 A340 aircraft in service with 45 operators worldwide. Lufthansa is the largest A340 operator with 27 aircraft in its fleet.

When Airbus designed the Airbus A300 during the 1970s it envisaged a broad family of airliners to compete against Boeing and McDonnell Douglas, two established US aerospace manufacturers. From the moment of formation, Airbus had begun studies into derivatives of the Airbus A300B in support of this long-term goal. Prior to the service introduction of the first Airbus airliners, Airbus had identified nine possible variations of the A300 known as A300B1 to B9. A tenth variation, conceived in 1973, later the first to be constructed, was designated the A300B10. It was a smaller aircraft that would be developed into the long-range Airbus A310. Airbus then focused its efforts on the single-aisle market, which resulted in the Airbus A320 family, which was the first digital fly-by-wire commercial aircraft. The decision to work on the A320, instead of a four-engine aircraft proposed by the Germans, created divisions within Airbus. As the SA or "single aisle" studies (which later became the successful Airbus A320) underwent development to challenge the successful Boeing 737 and Douglas DC-9 in the single-aisle, narrow-body airliner market, Airbus turned its focus back to the wide-body aircraft market.

The A300B11, a derivative of the A310, was designed upon the availability of "ten ton" thrust engines. Using four engines, it would seat between 180 and 200 passengers, and have a range of 6,000 nautical miles (11,000 km; 6,900 mi). It was deemed a replacement for the less-efficient Boeing 707s and Douglas DC-8s still in service. The A300B11 was joined by another design, the A300B9, which was a larger derivative of the A300. The B9 was developed by Airbus from the early 1970s at a slow pace until the early 1980s. It was essentially a stretched A300 with the same wing, coupled with the most powerful turbofan engine available at the time. It was targeted at the growing demand for high-capacity, medium-range, transcontinental trunk routes. The B9 offered the same range and payload as the McDonnell Douglas DC-10, but it used between 25% and 38% less fuel. The B9 was therefore considered a replacement for the DC-10 and the Lockheed L-1011 Tristar.

To differentiate the programme from the SA studies, the B9 and B11 were redesignated the TA9 and TA11 (SA standing for "single aisle" and TA standing for "twin aisle"). In an effort to save development costs, it was decided that the two would share the same wing and airframe; the projected savings were estimated at US$500 million (about £490 million or €495 million). The adoption of a common wing structure also had one technical advantage: the TA11's outboard engines could counteract the weight of the longer-range model by providing bending relief. Another factor was the split preference of those within Airbus and, more importantly, prospective airliner customers. Airbus vice president for strategic planning, Adam Brown, recalled,

North American operators were clearly in favour of a twin[jet], while Asians wanted a quad[jet]. In Europe, opinion was split between the two. The majority of potential customers were in favour of a quad despite the fact, in certain conditions, it is more costly to operate than a twin. They liked that it could be ferried with one engine out, and could fly 'anywhere'— ETOPS (extend-range twin-engine operations) hadn't begun then.