蒸汽机车，又称蒸汽火车，是以蒸汽机做为动力来源的铁路机车，也是铁路机车最早的发展类别。

蒸汽机车由蒸汽锅炉、汽机、车架、行走部、制动设备以及贮存燃料和水的煤水车等组成。

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.