The Austin-Healey 100 is a sports car built between 1953 and 1956 by the British Motor Corporation (the following model, named the 100-Six and built from 1956 to 1959, is a different car even though it shares the name "100"). It was developed by Donald Healey to be produced in-house by Healey's small car company in Warwick and based on Austin A90 Atlantic mechanicals. Healey built a single "Healey Hundred" for the 1952 London Motor Show, and the design impressed Leonard Lord, Managing Director of Austin so much that a deal was struck with Healey to build it in quantity at Austin's Longbridge factory. The car was renamed the Austin-Healey 100.

The "100" name comes from Donald Healey, who selected the name from the car's ability to reach 100 mph (160 km/h), as opposed to the Austin-Healey 3000, which is named for its 3000 cc engine.

100 (BN1 and BN2)

Production Austin-Healey 100s were finished at Austin's Longbridge plant alongside the A90 and based on fully trimmed and painted body/chassis units produced by Jensen in West Bromwich — in an arrangement the two companies previously had explored with the Austin A40 Sports. The first 100s (series "BN1") were equipped with the same 90 bhp (67 kW) engines and manual transmission as the stock A90, but the transmission was modified to be a three-speed unit with overdrive on second and top. The 2660 cc I4 engine featured an undersquare 87.3 mm (3.4 in) bore and 111.1 mm (4.4 in) stroke.

Girling 11 in (279.4 mm) drum brakes are fitted all round. Front suspension is independent using coil springs and at the rear is a rigid axle with semi elliptic leaf springs. The steering is by a cam and lever system.

A BN1 tested by The Motor magazine in 1953 had a top speed of 106 mph (171 km/h) and could accelerate from 0-60 mph (97 km/h) in 11.2 seconds. A fuel consumption of 22.5 miles per imperial gallon (12.6 L/100 km; 18.7 mpg_-US) was recorded. The test car cost £1063 including taxes.

These were built from May 1953, and replaced by the BN2 model in mid-1955.

The BN2 was fitted with a real 4-speed manual transmission, still with overdrive on the top 2 gears. Other features that distinguish the BN2 from the BN1 are the slightly larger front wheel arches, different rear axle and being the first 100 with optional two-tone paint. The color alternatives available to the 100 were: Reno Red, Spruce Green, Healey Blue, Florida Green, Old English White, Primrose Yellow, Black, and approximately 50 Gunmetal Grey cars. The BN2 two-tone colors were: White/Black; Reno Red/Black; Healey Blue/White; Black/Reno Red; and Florida Green/White.

In 1956, a BN2 100M (for Le Mans) model was developed as well, with larger carburetors, a cold air box to increase air flow to the carburetors, high-lift camshaft and 8.1:1 compression pistons. It produced 110 bhp (82 kW) at 4500 rpm. The front suspension was stiffened and the bonnet gained louvers, along with a bonnet belt. Most (approximately 70%) of the cars were finished with a two-tone paint scheme including two cars finished in unique color schemes: one White over Red and the other (for display at the 1955 London Motor Show) in Black over Pink. There were 640 factory built 100Ms—all 1956 model BN2s. The 100M components (except for the high compression pistons) were also available as a Le Mans kit which could be installed in either a BN1 or BN2 with the engine in situ, improving the power output to 100 bhp (75 kW) at 4500 rpm. The Donald Healey Motor Company at Warwick retrofitted 519 cars with the Le Mans kit after they had been delivered to the original owners. The Le Mans kit and its component parts could be ordered from BMC, so additional cars were modified by Austin dealers and private owners.

Built primarily with racing in mind, the aluminum-bodied "100S" (for Sebring) model developed 132 bhp (98 kW) at 4700 rpm. Only 50 production cars were made, plus an additional five works development/special test cars which were hand built by the Donald Healey Motor Company at Warwick. The cast iron cylinder head was replaced by one made from aluminum and the overdrive unit was not fitted to the gearbox. Dunlop disc brakes were fitted front and rear. To keep weight to a minimum, there were no bumpers or hood (convertible top), a smaller grille and the windscreen was plastic. The 100S was also the first production car in the world to sport disc brakes at both the front and rear . The car was approximately 200 lb (91 kg) lighter than standard. The majority of all 100S were two-toned White with Lobelia Blue sides. However, a handful of cars where ordered in Spruce Green, Reno Red and one single black 100S.

The final BN2 was produced in July 1956.