BSA started building bicycles in the 1880s and bicycle components, and followed with motorized bicycles in 1903. In 1907, BSA acquired parts maker Eadie Manufacturing (created by Albert Eadie, general manager of Royal Enfield). They made their first own real motorcycle in 1910, a 499cc side-valve. Model H and Model K were their pre-war singles.

Production ceased during WW1 while they pursued their traditional manufacturing, making guns, but returned quickly after the war, making their first V-twins in 1919. In the early 1920s, they acquired an engineer and designer from Daimler called Harold Briggs who designed new sporting machines for them, including their popular 493cc ohv Sloper of 1928. They made their first and only two-stroke, a 175cc unit construction bike, for only one season, in 1928. BSA's famous Star series started in the 1930s with the Blue Star singles in  250, 350 and 500cc versions. The Empire Stars followed. Val Page, formerly of Ariel, then Triumph, joined BSA to make their M-range in the late 1930s.

Reliable rather than innovative, BSA sold 126,334 military M20 sv bikes to the Allied war effort, as well as munitions, shell fuses and a folding bicycle, and soon owned 67 factories. German bombs destroyed most of their original 1863 and 1915 premises, killed 53 workers and destroyed 1,600 machine tools. In the 1930s, the company boasted that one in four motorcycles on the roads in the UK was a BSA.

BSA became the largest motorcycle company in the world between the wars. In 1939, the company owned 67 factories across the UK. During the war, they made 126,000 M20 motorcycles - among their other war production! They were so large that they bought Triumph in 1951. They also took over Sunbeam from AMC in 1936 (1943?) and Ariel in 1944. BSA also acquired New Hudson. In 1946 they announced a new competition model, the 350cc B31.

BSA's most famous single, the 499cc ohv DBD34 Gold Star, started production in 1931 as the Blue Star. This became the Empire Star in 1937. It was renamed after Walter Handley won a Gold Star at Brooklands that year and Val Page took over the re-design. Production of the new Gold Star began in 1938 and continued until 1963. In that time the Goldie dominated many races including the Isle of Man Clubmans TT. It was replaced with smaller singles, the 250cc C15, which later grew to 500cc.

A popular BSA staple was the vertical twin. It began as the 500cc A7 in 1946, followed by the Bert Hopwood-engineered 650cc A10 in 1950 and a re-designed 500 called the Star Twin, which won the Maudes Trophy in 1952 for exceptional endurance . These twins were replaced by the unit-construction 500cc A50 and 650cc A65 twins in 1962. The A50 had several names, including the Royal Star. The rare Rocket Gold Star of 1962 was a specially-tuned A10 with Gold Star forks, brakes and wheels. The 1965 Spitfire 650cc was a sports twin (built until 1968), followed by the A65L Lightning dual-carb version. 650cc twins stopped production in 1971, the 500cc was retained until 1972. 

Another popular BSA was the diminutive Bantam, based on a German DKW RT125 design.

During the 1960s, the company was slow to innovate, and made several failures, including the Dandy and Beagle commuter bikes and the Ariel-3 tricycle. Profits were falling from their 1960 high of 9 million pds. In 1962, BSA followed Triumph to make unit construction twins, the A50 and A65. In 1968 they adopted triumph's twin-leading-shoe drum brakes. The Rocket Three was BSA's triple, which appeared at the same time as Triumph's Trident, in 1969. The engine was basically a Trident, sloped at 15 degrees, but the frame was BSA's.  It offered a glimmer of hope for BSA's future, but production on the Fury/Triumph Bandit broke them.

Although an industrial giant, the company proved unable to compete well against the Japanese, and by 1970 they hit financial hardships. The 1971 lineup saw major makeovers, including oil-in-frame 650 twins. BSA was bought by Norton (owned by Manganese Bronze) and absorbed into the Norton-Villiers-Triumph group in 1971, which managed to design an uncomfortably high A65 Lightning at Umberslade Hall before BSA collapsed. The name was finally abandoned and production ended in 1973. 

The UK rights to the BSA name was acquired by the Canadian Aquilini family. BSA Co. was sold and a US company (Bill Colquhuon's BSA Co.) used the name for Rotax-engined military bikes and Yamaha-based Bushman machines for developing nations. In 1991, Andover Norton and BSA Co. merged to create BSA Group, which was taken over in 1994 to form BSA Regal. They announced a new Gold SR using a Yamaha SR400 engine in a Gold Star styled chassis. See www.bsa-regal.co.uk.