Abstract: A fastener driving tool is provided including a portable housing defining a fastener drive track, a fastener driving element carried by the housing for movement within the drive track through successive cycles of operation, each of which includes a fastener driving stroke and a return stoke, and a drive piston operatively connected with the fastener driving element for movement therewith. The tool also has a magazine assembly carried by the housing for receiving a supply of fasteners and feeding successive fasteners into the drive track in a position to be driven into a work piece during successive fastener driving strokes of the fastener driving element, an actuating structure carried by the housing and being constructed and arranged to move from a normal, inoperative position into an operative position to initiate the movement of the drive piston and the fastener driving element through a fastener driving stroke, and an overdrive signaling structure carried by the housing.