Armstrong Siddeley was a British engineering group that operated during the first half of the 20th century. It was formed in 1919 and is best known for the production of luxury vehicles and aircraft engines.

The company was created following the purchase by Armstrong Whitworth of Siddeley-Deasy, a manufacturer of luxury motor cars that were marketed to the top echelon of society. After the merge of companies, this focus on quality continued throughout in the production of cars, aircraft engines, gearboxes for tanks and buses, rocket and torpedo motors, and the development of railcars. Company mergers and takeovers with Hawker Aviation and Bristol Aero Engines saw the continuation of the car production which ceased in August 1960.

The company was absorbed into the Rolls-Royce conglomerate which was interested in the aircraft and aircraft engine business. Eventually, the remaining spares and all motor car interests were sold to the Armstrong Siddeley Owners Club Ltd, which now owns the patents, designs, copyrights and trademarks, including the name Armstrong Siddeley.

Considered "an elegant car appropriate for royal use", the "Armstrong Siddeley Saloon" was used by the Prince of Wales (later King Edward VIII) during his 1930 tour of Uganda.