An actuator-damper unit for use in orthotic or prosthetic devices. The actuator-damper unit includes a housing which may be fastened on the orthotic or prosthetic device and in which a cylinder is formed. A first piston is displaceably mounted in the cylinder and is coupled to a piston rod. The piston rod is disposed, via a first end, on the first piston and may be coupled, via a second end, to the orthotic or prosthetic device. The first piston separates two fluid chambers in the cylinder from each other and forms a piston-cylinder unit, wherein at least one further piston is coupled to the first piston in order to form at least one further, variable-volume fluid chamber.
