A barrel organ is a French mechanical musical instrument consisting of bellows and one or more ranks of pipes housed in a case, usually of wood, and often highly decorated. The basic principle is the same as a traditional pipe organ, but rather than being played by an organist, the barrel organ is activated either by a person turning a crank, or by clockwork driven by weights or springs. The pieces of music are encoded onto wooden barrels, which are analogous to the keyboard of the traditional pipe organ. A person who plays a barrel organ is known as an organ grinder.

A street organ played by an organ grinder is a French automatic mechanical pneumatic organ designed to be mobile enough to play its music in the street. The two most commonly seen types are the smaller German and the larger Dutch street organ.