An electro-mechanical actuator having an electric motor (12), a member (15) rotatable by the electric motor, a first pin and slot connection (17, 18) connecting the rotatable member with a pivoting rocker lever (19) and a pivoting connection (21,22) connecting the rocker lever (19) or rotatable member (15) with a linearly moveable operating member (23) so that rotation of the rotatable member (15) by the motor (12) gives linear movement (X) of the operating member between two end travel positions. Bias means (24, 25) are operative on the rocker lever (19) to assist the motor (12) to move the operating member (23) to one of its end travel positions and to hold the operating member in its other end travel position. The actuator is particularly suitable for operating a vehicle driveline clutch with the operating member (23) moveable between an extended end travel position in which the clutch is disengaged and its other retracted end travel position in which the clutch is engaged. In this application the line of action (F) of the bias means (24, 25) acting on the rocker arm (19) can move over-centre relative to the axis of pivoting (G) of the rocker arm when the clutch is in closed position so that the biasing means also holds the clutch in its closed position.