A generalized source method is presented for the resolution of the problem of monochromatic wave propagation in non-homogeneous, isotropic structures. When implemented in the form of an iterative technique, it is demonstrated to give the exact analytical solution of the known problem of propagation in a two half-space structure. When implemented in the form of an integral expression, it is shown to give an exact solution under a normalized numerical convergence criterion. It thus represents a new powerful method for electromagnetic wave propagation in arbitrary structures, and also for the assessment of other resolution techniques proposed so far in optical wave propagation, diffraction and scattering.