Abstract: An electromechanical locking system (8) comprises a lock (12) and a key (14). The lock includes a cylinder (16), an electronic control unit (18) which is housed within the cylinder, a tailpiece (20), and an electrically-operable clutch mechanism (22) which is housed within the cylinder (16). The cylinder (16) is rotatably mounted to a first component to be locked and the tailpiece includes an adapter (24) which is operable to interfere with the movement of a second component to be locked to the first component. The control unit (18) draws power from the key and is operable to generate an actuation signal for actuating the clutch mechanism (22) which releasably connects the cylinder and the tailpiece when actuated, thereby causing them to become rotatably coupled.