Abstract: A corner joint system for fastening two perpendicular furniture panels to form a box corner includes first and second male connector rails and a female connector rail. The male connector rails each include a base having a longitudinal spline extending inwardly from an inner surface. The male connector rails are secured in adjacent relation to adjacent corner surfaces of the furniture panels such that the respective splines are arranged in adjacent perpendicular relation. The female connector rail includes a main body portion having an upper end and a lower end, and two perpendicular, longitudinal, spline channels extending upwardly through the main body portion from the lower end to the upper end. The spline channels of the female connector rail are slidably received in interfitting relation over the adjacent splines of the male connector rails to cooperatively capture the splines and interlock the rails, forming a rigid, right angle box corner.