A steam motor is a form of steam engine used for light locomotives and light self-propelled motor cars used on railways. The origins of steam motor cars for railways go back to at least the 1850s, if not earlier, as experimental economizations for railways or railroads with marginal budgets. These first examples, at least in North America, appear to have been fitted with light reciprocating engines, and either direct or geared drives, or geared-endless chain drives. Most incorporated a passenger carrying coach attached to the engine and its boiler. Boiler types varied in these earlier examples, with vertical boilers dominant in the first decade and then with very small diameter horizontal boilers. Other examples of steam motor cars incorporated an express-baggage or luggage type car body, with coupling apparatus provided to allow the steam motor car to draw a light passenger coach.

High-speed steam engines were one of the final developments of the stationary steam engine. They ran at a high speed, of several hundred rpm, which was needed by tasks such as electricity generation.