The Airbus A330 is a wide-body airliner developed and produced by Airbus. Airbus began developing larger A300 derivatives in the mid–1970s, giving rise to the A330 twinjet as well as the Airbus A340 quadjet, and launched both designs along with their first orders in June 1987. The A330-300, the first variant, took its maiden flight in November 1992 and entered service with Air Inter in January 1994. The A330-200, a shortened longer-range variant, followed in 1998 with Canada 3000 as the launch operator.

The A330 shares many underpinnings with the airframe of the early A340 variants, most notably the same wing components, and by extension the same structure. However, the A330 has two main landing gear legs instead of three, lower weights, and slightly different fuselage lengths. Both airliners have fly-by-wire controls as well as a similar glass cockpit to increase the commonality. The A330 was Airbus's first airliner to offer a choice of three engines: the General Electric CF6, Pratt & Whitney PW4000, or the Rolls-Royce Trent 700. The A330-300 has a range of 11,750 km (6,340 nmi; 7,300 mi) with 277 passengers, while the shorter A330-200 can cover 13,450 km (7,260 nmi; 8,360 mi) with 247 passengers. Other variants include the A330-200F dedicated freighter, the A330 MRTT military tanker, and the ACJ330 corporate jet. The A330 MRTT was proposed as the EADS/Northrop Grumman KC-45 for the US Air Force's KC-X competition, but lost to the Boeing KC-46 in appeal after an initial win.

In July 2014, Airbus announced the re-engined A330neo (new engine option) comprising A330-800 and -900, which entered service with TAP Air Portugal in December 2018. With the exclusive, more efficient Trent 7000 turbofan and improvements including sharklets, it offers up to 14% better fuel economy per seat. The first-generation A330s (-200, -200F, and -300) are now called A330ceo (current engine option).

Delta Air Lines is the largest A330 family operator with 81 aircraft in its fleet as of September 2025^[update]. A total of 1,943 orders have been placed for the A330 family, of which 1,643 have been delivered and 1,464 are in service with 149 operators. The global A330 fleet had accumulated more than 65 million flight hours since its entry into service. The A330 is the second most delivered wide-body airliner after the Boeing 777. It competes with larger variants of the Boeing 767, smaller variants of the 777, and the 787. It is complemented by the larger Airbus A350, which succeeded the four-engined A340. As of June 2024^[update], the Airbus A330 has been involved in 46 aviation accidents and incidents, including 14 hull-losses (ten due to flight related accidents and four due to criminal related accidents), for a total of 339 fatalities.

Airbus's first airliner, the A300, was envisioned as part of a diverse family of commercial aircraft. Pursuing this goal, studies began in the early 1970s into derivatives of the A300. Before introducing the A300, Airbus identified nine possible variations designated B1 through B9. A tenth variant, the A300B10, was conceived in 1973 and developed into the longer-range Airbus A310. Airbus then focused its efforts on single-aisle (SA) studies, conceiving a family of airliners later known as the Airbus A320 family, the first commercial aircraft with digital fly-by-wire controls. During these studies Airbus turned its focus back to the wide-body aircraft market, simultaneously working on both projects.

In the mid 1970s, Airbus began development of the A300B9, a larger derivative of the A300, which would eventually become the A330. The B9 was essentially a lengthened A300 with the same wing, coupled with the most powerful turbofan engines available. It was targeted at the growing demand for high-capacity, medium-range, transcontinental trunk routes. Offering the same range and payload as the McDonnell Douglas DC-10 but with 25 per cent better fuel efficiency, the B9 was seen as a viable replacement for the DC-10 and the Lockheed L-1011 TriStar trijets. It was also considered as a medium-ranged successor to the A300.

At the same time, a 200-seat four-engine version, the B11 (which would eventually become the A340) was also under development. The B11 was originally planned to take the place of narrow-body Boeing 707s and Douglas DC-8s then in commercial use, but would later evolve to target the long-range, wide-body trijet replacement market. To differentiate from the SA series, the B9 and B11 were re-designated as the TA9 and TA11, with TA standing for "twin aisle". Development costs were reduced by the two aircraft using the same fuselage and wing, with projected savings of US$500 million. Another factor was the split preference of those within Airbus and, more importantly, those of prospective customers; twinjets were favoured in North America, quad-jets desired in Asia, and operators had mixed views in Europe. Airbus ultimately found that most potential customers favoured four engines for their exemption from existing twinjet range restrictions and their ability to be ferried with one inactive engine. As a result, development plans prioritised the four-engined TA11 ahead of the TA9.

The first specifications for the TA9 and TA11, aircraft that could accommodate 410 passengers in a one-class layout, emerged in 1982. They showed a large underfloor cargo area that could hold five cargo pallets or sixteen LD3 cargo containers in the forward, and four pallets or fourteen LD3s in the aft hold—double the capacity of the Lockheed L-1011 TriStar or DC-10, and 8.46 metres (27.8 ft) longer than the Airbus A300. By June 1985, the TA9 and TA11 had received more improvements, including the adoption of the A320 flight deck, digital fly-by-wire (FBW) control system, and side-stick control. Airbus had developed a common cockpit for their aircraft models to allow quick transition by pilots. The flight crews could transition from one type to another after only one week's training, which reduces operator costs. The two TAs would use the vertical stabiliser, rudder, and circular fuselage sections of the A300-600, extended by two barrel sections.