In this paper, the principal elements of the full-wave solution and its direct analytical links to the physical-optics and small-perturbation solutions are reviewed succinctly. Thus a two-step analytical procedure that transforms Rice's ''first-order'' small-perturbation solution into the physical optics solution is prescribed. Questions of convergence raised by Rice himself are also addressed since the small-perturbation solution (when applied to random rough surfaces) diverges as the slope parameter becomes small and smaller. Furthermore, it is shown that the ''exact numerical result'' based on the moments method do not include the diffraction term, while the corresponding full-wave results, used for comparison do not include the diffraction term. No true comparisons can be made between the full-wave solution and the small-perturbation solution unless the excitations assumed in both cases are the same and unless the diffraction term is not added to the full-wave solution for the diffusely scattered field. ¿American Geophysical Union 1991