Abstract: A biscuit joiner for cutting semi-elliptical slots in opposing edges of workpieces which are to be joined along those edges includes a housing adapted to be mounted upon the quill of a multi-purpose woodworking tool, which housing encloses a rotary saw blade adapted to be attached to a spindle projecting from the quill on which the housing is mounted. A spring loaded guide projects from the front face of the housing and has a slot therethrough, so that when the front face of the guide is engaged by an edge of a workpiece to be slotted the guide can be pushed inwardly against spring pressure, allowing the rotary saw blade to be exposed and form a slot in the edge of the workpiece. Adjustable stops are provided on the guide so that a desired depth of cut will automatically be made after adjustment.