The simple thin-film optical method is generalized to take into account intermode coupling and oblique incidence in a plane stratified magnetoionic medium. In analogy with the simple thin-film optical method, all partial reflections within a thin, elementary layer are given as a geometric series of matrix products, which are summed to yield the over-all transfer coefficient matrices of the elementary layer in terms of the characteristic waves of the medium (off-diagonal elements representing the over-all intermode coupling coefficients). The analysis is extended by an iterative procedure, layer by layer, starting high in the ionosphere and terminating at the ionospheric base to yield the over-all transmission and reflection coefficient matrices of the medium. The ‘reverse iteration,’ starting low and extending upward, yields transfer coefficient matrices of intermediate ionospheric slabs but at the price of a more complex iteration procedure. The method is free of the tendency to numerical swamping and in the case of normal incidence simplifies considerably. Applications to LF and hydromagnetic wave propagation in the lower ionosphere are given.