A generalized analysis of wave propagation in periodic layered media is applied to the special case of optical surface waves. These waves, confined to the interface between a periodic layered medium and a homogeneous medium, are formally analogous to electronic surface states in crystals. Single‐mode surface‐wave propagation along the surface of a GaAs‐AlGaAs multilayer stack (grown by molecular‐beam epitaxy) has been observed experimentally.