In a control system for a lower limb prosthesis or orthosis, a plurality of sensors generate sensor signals representing kinematic measurements (21) relating to the movement of segments of a prosthesis or orthosis (e.g. a thigh segment and a shank segment). The sensor signals are applied in a comparison stage 22 to a plurality of comparison steps (K1, K2, K3) which produce binary outputs for feeding to a combining stage (23) in which a binary word (16) is produced, identifying a phase of limb motion. During a walking cycle, for instance, the binary word (16) changes, and the sequence of words represents a movement phase description which is used as the input for a prosthetic or orthotic movement controller.