Abstract: A self-energizing self-levelling controllable damper unit is provided for use in a vehicle suspension system connected between two relatively movable portions of the system. The unit includes a piston and cylinder arrangement containing a damping fluid and defining three chambers of variable volume dependent upon the relative positions of the components of the arrangement. A valve is provided to regulate the flow of the damping fluid between the first and the second chambers, and between the second and third chambers respectively. The valve is controlled by a controller which, as the vehicle drives over a road surface, controls relative movement of the components of the piston and cylinder arrangement by permitting the damping fluid to flow from the third chamber to the second chamber and thence to the first chamber, and vice versa, until a desired ride height of the vehicle is achieved.