A switcher (American English) or shunter (British English), is a type of small locomotive used for maneuvering railway vehicles over short distances. Switchers do not usually move trains over long distances, instead they typically assemble trains in order for another locomotive to take over. Switchers often operate in a railyard or make short transfer runs. They may serve as the primary motive power on short branch lines or switching and terminal railroads.

Switchers are optimized for their role, being relatively low-powered but with a high starting tractive effort for getting heavy cars rolling quickly. Switchers are geared to produce high torque but are restricted to low top speeds and have small diameter driving wheels. Switchers tend to be durable and to remain in service for a long time, such as the Swedish class U.

American, Russian, Indian and Chinese switchers tend to be larger, with bogies to allow them to be used on tight radiuses. Western European shunters tend to be smaller and more often have fixed axles. They also often maintained coupling rods for longer than other locomotive types, although bogie types have long been used where very heavy loads are involved, such as at steelworks.