A uniform geometrical theory of diffraction solution is developed for the two-dimensional problem of high-frequency plane wave diffraction by a planar junction of two thin dielectric/ferrite half planes. Each material half plane in this two-part configuration is assumed to be electrically thin so that it can be replaced in the analysis by a generalized resistive boundary condition of 0(t), where t is the corresponding material slab thickness. The solution obtained is based on the Wiener-Hopf technique, and it is shown that the present boundary value problem can be completely solved by imposing a junction condition at the junction of the two dielectric half planes in addition to the boundary and radiation conditions as well as the usual edge condition. This junction condition can be obtained if the field near the junction is modeled by a quasi-static solution. The solution developed here can be further specialized to limiting cases for which either of the material half planes can become free space, perfectly conducting, or purely resistive, respectively. Several numerical examples are presented, and it is shown that the present solution reduces to known results and agrees very well with a moment method solution.