Abstract: A fastener driving tool which employs an activating mechanism, which mechanism will only be effective to fire the tool if operated in the proper sequence. The activating mechanism includes a trigger assembly and a bottom trip mechanism which is operable when the tool is placed in contact with the workpiece. The trigger mechanism is designed so that it will only operate to fire the tool if it is moved after the tool has been placed in contact with the workpiece. Pulling of the trigger before the workpiece is contacted will prevent firing of the tool. The trigger mechanism is also designed so that it includes an arrangement whereby once the tool has been fired the tool can be fired repeatedly upon repeated contact of the tool with the workpiece.