The mortise and tenon joint is one of the most fundamental joinery techniques used in woodworking because it is both simple and strong. It is what separates “IKEA-style regurgitated termite barf” from fine furniture. Although there are many variations on that joint, the basic mortise and tenon is comprised of a male piece — the tenon — and a female piece — the mortise. The photos below show how I usually cut a square mortise using a plunge router, a custom made jig and a chisel. The plan for the jig can be found in issue #90 of ShopNotes magazine. (Click on the thumbnails below to see a larger version of each photo.)