The Airbus A321 is a stretched first derivative of the standard A320. The variant was launched in 1988, when the A320 began operations. Compared with the A320, the A321's major change is the stretched fuselage, which is lengthened by 6.94 metres (22 ft 9 in); the A321 is the largest of the A320 family. This is achieved by adding a front plug immediately forward of wing 4.27 m (14 ft 0 in), and a 2.67 m (8 ft 9 in) rear plug. To maintain performance, double-slotted flaps were included, in addition to increasing the wing area by 4 m2 (43 sq ft), to 128 m2 (1,380 sq ft). Other minor modifications were made to accommodate the A321's 9,600 kg (21,200 lb) increase in maximum takeoff weight to 83,000 kg (183,000 lb). The maiden flight of the first of two prototypes came on 11 March 1993. The A321 entered service in 1994.

The basic A321-100 features a reduction in range compared to the A320 as extra fuel tankage was not added to the initial design to compensate for the extra weight. To overcome this Airbus launched the heavier and longer range A321-200 development in 1995 which has a full-passenger transcontinental US range. This is achieved through higher thrust engines (V2533-A5 or CFM56-5B3), minor structural strengthening, and greater fuel capacity with the installation of one 26,600 L (7,000 US gal) in the rear underfloor hold, or two 29,684 L (7,842 US gal) tanks. The A321-200 first flew in December 1996. Its direct competitor is the 757-200 and the 737-900/900ER.