A downhole valve (10) comprises a body (12) defining a through bore (14) and a valve seat (16, 17); and a valve member (18) mounted in the body and moveable between positions to open and close the body bore (14). The valve member (18) defines a segment of a wall of a hollow sphere. In the open position the valve member (18) is located to one side of the bore (14) and in the closed position the valve member (18) engages the valve seat (16, 17).
