The Mini is a very small two-door, four-seat car, produced for four decades over a single generation, with many names and variants, by the British Motor Corporation (BMC) and its successors British Leyland and the Rover Group, and finally (briefly) under BMW ownership. Minis were built as fastbacks,^{[citation needed]} estates, convertibles, and various other body styles. Minus a brief 1990s hiatus, from 1959 into 2000, an estimated 5.38 million of all variations combined were built, and the Mini's engines also powered another 2 million Mini Metros, though the Mini eventually outlasted its successor.

Initially, the Mini was marketed under the Austin and Morris names, as the Austin Seven and Morris Mini-Minor; the Austin Seven was renamed Austin Mini in 1962 and Mini became a marque in its own right in 1969. Retrospectively, the car is known as the "Classic Mini" to distinguish it from the modern MINI family of vehicles produced since 2001 by German carmaker BMW, who took ownership of the Mini name following the sale of Rover Group in 2000.

This distinctive two-door car was designed for BMC by Sir Alec Issigonis. Its space-saving transverse engine and front-wheel drive layout – allowing 80% of the area of the car's floorpan to be used for passengers and luggage – influenced a generation of car makers. The front-wheel-drive, transverse-engine layout were used in many other "supermini" style car designs such as Honda N360 (1967), Nissan Cherry (1970), and Fiat 127 (1971). The layout was also adapted for larger subcompact designs. In 1999, the Mini was voted the second-most influential car of the 20th century, behind the Ford Model T, and ahead of the Citroën DS and Volkswagen Beetle. It is also considered an icon of 1960s British popular culture.

The Mini Mark I had three major UK updates: the Mark II, the Clubman, and the Mark III. Within these was a series of variations, including an estate car, a pick-up, a van, and the Mini Moke, a jeep-like buggy. The performance versions, the Mini Cooper and Cooper "S", were successful as both race and rally cars, winning the Monte Carlo Rally in 1964, 1965, and 1967. The Mini was manufactured in England at the Longbridge plant in Birmingham located next to BMC's headquarters and at the former Morris Motors plant at Cowley, as well as in Australia (Victoria Park/Zetland BMC Australia factory) and later also in Spain (Authi), Belgium, Italy (Innocenti, as the Innocenti Mini), Chile, Malta, Portugal, South Africa, Uruguay, Venezuela, and Yugoslavia (IMV). In 1980, British Leyland launched the Mini's follow-up, the Austin Metro, however the Mini outlasted it and continued to be produced at Longbridge until October 2000.

The Mini came about because of a fuel shortage caused by the 1956 Suez Crisis. Petrol was once again rationed in the UK, sales of large cars slumped, and the market for German bubble cars boomed, even in countries such as the United Kingdom, where imported cars were still a rarity.

Leonard Lord, the head of BMC, reportedly detested these cars so much that he vowed to rid the streets of them and design a 'proper miniature car'. He laid down some basic design requirements – the car should be contained within a box that measured 10×4×4 feet (3.0×1.2×1.2 m); and the passenger accommodation should occupy 6 feet (1.8 m) of the 10-foot (3.0 m) length; and the engine, for reasons of cost, should be an existing unit.

Alec Issigonis, who had been working for Alvis, had been recruited back to BMC in 1955 with a brief from Lord to design a range of technically advanced family cars in the same innovative spirit as his earlier Morris Minor to complement BMC's existing conventional models. Issigonis had set out design projects for three cars – large and small family cars and a very small economy car. His initial work was on the largest car, designated XC9001, with the smallest car, XC9003, having the lowest priority despite it being Issigonis' greatest personal interest. With Lord's dictum to produce a bubble car competitor and his revised design requirements being laid down in October 1956, work on XC9001 stopped and XC9003 became the priority. In addition to Issigonis, the team that developed the Mini included John Sheppard (who had worked with Issigonis at Alvis), Jack Daniels (who had worked with Issigonis on the Morris Minor), Chris Kingham (also from Alvis), Charles Griffin (from Cowley), Vic Everton (from the body—jig shop), Ron Dovey (who built the bodies), Dick Gallimore (who laid out the experimental bodies), and George Cooper (whose job was to check the layouts). Together, by July 1957, they had designed and built the original XC9003 prototype, which was affectionately named the "Orange Box" because of its colour. Leonard Lord approved the car for production on 19 July and XC9003 became project ADO15.

The ADO15 used a conventional BMC A-Series four-cylinder, water-cooled engine, but departed from tradition by mounting it transversely, with the engine-oil lubricated, four-speed transmission in the sump, and by employing front-wheel drive. Drive was taken down to the transmission via a conventional clutch coupled to a set of primary gears on the end of the crankshaft which gave rise to the characteristic transmission "whine" for which the Mini became famous. Almost all small front-wheel drive cars developed since have used a similar configuration, except with the transmission separately enclosed rather than using the engine oil and mounted directly onto the end of the crankshaft, but with unequal length driveshafts. The radiator was mounted at the left side of the car so that the engine-mounted fan could be retained, but with reversed pitch so that it blew air into the natural low pressure area under the front wing. This location saved vehicle length, but had the disadvantage of feeding the radiator with air that had been heated by passing over the engine. It also exposed the entire ignition system to the direct entry of rainwater through the grille. Early prototypes used the existing 948 cc A-Series unit, but this provided the ADO15 with performance far greater than its price and purpose required – a top speed of about 80 mph (129 km/h). The engine was reduced to a new 848 cc capacity with a shorter stroke. This reduced power from 37 to 33 bhp and caused a significant drop in torque, so provided more realistic performance, especially when the ADO15 body was widened by 2 inches (5.08 cm) over the XC9003 prototype, which blunted the car's top speed while improving its stability and roadholding. Even so, the ADO15 had a top speed of 75 mph (121 km/h), which was better than many other economy cars of the time.