An actuator assembly comprising: a first part; a second part that is movable relative to the first part; and one or more actuating units each configured to apply an actuating force to the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; a bearing arrangement between the body portion and the first or second part and arranged to guide movement of the body portion relative to the first or second part in an actuating plane; an SMA element connected between the body portion and the first part, and arranged, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the first part and configured to modify the input force so as to give rise to the actuating force.