The A318, also known as the "Mini-Airbus" or "baby bus", is the smallest member of the A320 family, and the smallest Airbus of any kind. It originated from the AVIC and Airbus Industrie Asia cooperation program AE31X. During development, it was known as the "A319M3," thus indicating its history as a direct derivative of the A319. "M3" indicates "minus three fuselage frames." The aircraft is six metres shorter and 14 tonnes lighter than the A320. To compensate for the reduced moment arm it has a larger vertical stabilizer, making it 80 centimetres taller than the other A320 variants. Pilots who are trained on the other variants may fly the A318 with no further certification, since it features the same type rating as its sister aircraft.
The A318 has a passenger capacity of 109 in a two-class configuration. It is intended to replace early Boeing 737 and Douglas DC-9 models, though it is also a rival to the 737-600. Boeing also offered their 717 aircraft as a competitor, although it was suitable primarily for regional routes and did not have the A318's range capabilities.