A gate valve for mounting in a pipeline comprises a valve body and a gate mounted in the valve body so as to be movable between an open position, and a closed position where a valve opening formed in the valve body is closed by the gate. The gate comprises two opposed faces spaced from the transverse plane of the gate, at least one face being provided with at least two seals that each extend around the face one seal being located within the periphery of the other such that both seals, when the gate is in the closed position, seal against a seat of the valve body to seal against the pressure of fluid acting on the gate in use. In one embodiment, a gate has four seals in total, two on the upstream gate face and two on the downstream gate face.