in music, on the organ, mechanical system that transmits the organist's action in depressing a key to the pallet valve that admits air into the pipes that the key controls. It consists of cranks, levers, and trackers (thin strips of wood connecting, under tension, parts of the organ action and conveying motion from one part to another).

On large organs with many stops and couplers, considerable manual strength is needed to operate the system and overcome wind pressure against the valve. In contrast to lighter 19th- and 20th-century pneumatic and electric actions, however, tracker action gives the player direct contact with the valve, resulting in a more sensitive touch. A revival of tracker action began in about 1925.