Abstract: A fulcrum lock for preventing substantial movement of a window sash when wind forces are directed against the sash. The sash includes a frame that is contained in an outer window frame. The fulcrum lock has an elongated main body provided with a fulcrum or pivot surface located between the ends of the main body, and legs that extend generally perpendicular to the extent of the main body. The fulcrum lock is located in one of the sash or window frames, while the other of said frames is provided with an opening located to receive one of the ends of the fulcrum lock when the other end is engaged by the frame containing the opening.