Abstract: A controllable motion damper with a damping piston separating two damping chambers from each other in a damping cylinder. A damping valve is disposed in a connecting channel of the two damping chambers with the transmissivity of the damping valve for a damping fluid contained in the motion damper being controlled by a control device. Both damping chambers are filled with an electromagnetically uninfluenceable damping fluid. The control device includes a slide piston unit filled with a magnetorheological fluid. The slide piston unit includes a slide piston operatively coupled to the damping piston, wherein, through the intermediary of the magnetorheological fluid, the magnetorheological fluid is influenceable by controllable magnetic field generators with regard to its flow resistance with the slide piston acting on an actuator connected to the damping valve for controlling the movement of the damping piston.