A steam locomotive is a railway locomotive that produces its pulling power through a steam engine. These locomotives are fueled by burning combustible material—usually coal, wood, or oil—to produce steam in a boiler. The steam moves reciprocating pistons which are mechanically connected to the locomotive's main wheels (drivers). Both fuel and water supplies are carried with the locomotive, either on the locomotive itself or in wagons (tenders) pulled behind. The first steam locomotive, made by Richard Trevithick, first operated on 21 February 1804, three years after the road locomotive he made in 1801.

Steam locomotives were first developed in Great Britain during the early 19th century and dominated railway transport until the middle of the 20th century. From the early 1900s they were gradually superseded by electric and diesel locomotives, with full conversions to electric and diesel power beginning from the 1930s. The majority of steam locomotives were retired from regular service by the 1980s, though several continue to run on tourist and heritage lines.