An automatic transmission (AT) or automatic gearbox is a multi-speed transmission used in motor vehicles that does not require any input from the driver other than throttle position to change forward gears under normal driving conditions.
The 1904 Sturtevant "horseless carriage gearbox" is often considered to be the first true automatic transmission. The first mass-produced automatic transmission is the General Motors Hydramatic four-speed hydraulic automatic, which was introduced in 1939.