The present invention provides a gravity gradiometer which comprises at least one sensor mass suspended by a coupling which enables movement of the at least one sensor mass about an axis in response to a gravity gradient. Further, the gravity gradiometer comprises at least one transducer for generating an electrical signal in response to the movement of the at least one sensor mass relative to a component of the transducer and for influencing the movement of the at least one sensor mass. The gravity gradiometer also comprises electrical circuitry for receiving the electrical signal from the at least one transducer and for directing an actuating signal to the at least one transducer so that in use the at least one transducer functions as sensor and actuator.