An instrument for positioning a cup component of an orthopaedic joint prosthesis, comprising: an actuator; and a plurality of jaw members (152, 154, 156, 158) arranged around a longitudinal axis of the instrument, each jaw member having: a mounting end, a gripping end with a transversely extending member directed inwardly which can be received in a recess (186, 188, 190, 192) in an outwardly facing side wall of a cup component, wherein the gripping end of each of the jaw members includes a flat underside surface arranged to engage an upper surface of a rim of the cup component and can be displaced between a retracted position and a deployed position in which the gripping end is displaced from the retracted position in the direction in which the transversely extending member is directed, and a surface between the mounting end and the gripping end which is inclined to the longitudinal axis of the instrument and curved in an outward direction away from the longitudinal axis and in a peripheral direction around the longitudinal axis, wherein the actuator and the plurality of jaw members are capable of relative movement along the longitudinal axis of the instrument with the actuator in contact with the inclined surfaces of the jaw members so that said relative movement causes the jaw members to move between their retracted position and deployed position. an actuator; and a plurality of jaw members (152, 154, 156, 158) arranged around a longitudinal axis of the instrument, each jaw member having: a mounting end, a gripping end with a transversely extending member directed inwardly which can be received in a recess (186, 188, 190, 192) in an outwardly facing side wall of a cup component, wherein the gripping end of each of the jaw members includes a flat underside surface arranged to engage an upper surface of a rim of the cup component and can be displaced between a retracted position and a deployed position in which the gripping end is displaced from the retracted position in the direction in which the transversely extending member is directed, and a surface between the mounting end and the gripping end which is inclined to the longitudinal axis of the instrument and curved in an outward direction away from the longitudinal axis and in a peripheral direction around the longitudinal axis, wherein the actuator and the plurality of jaw members are capable of relative movement along the longitudinal axis of the instrument with the actuator in contact with the inclined surfaces of the jaw members so that said relative movement causes the jaw members to move between their retracted position and deployed position. a mounting end, a gripping end with a transversely extending member directed inwardly which can be received in a recess (186, 188, 190, 192) in an outwardly facing side wall of a cup component, wherein the gripping end of each of the jaw members includes a flat underside surface arranged to engage an upper surface of a rim of the cup component and can be displaced between a retracted position and a deployed position in which the gripping end is displaced from the retracted position in the direction in which the transversely extending member is directed, and a surface between the mounting end and the gripping end which is inclined to the longitudinal axis of the instrument and curved in an outward direction away from the longitudinal axis and in a peripheral direction around the longitudinal axis, wherein the actuator and the plurality of jaw members are capable of relative movement along the longitudinal axis of the instrument with the actuator in contact with the inclined surfaces of the jaw members so that said relative movement causes the jaw members to move between their retracted position and deployed position.