Abstract: A reasonable quantum electrodynamical model is introduced in the present article for the interacting system of a planar waveguide and the electromagnetic field. The response to external electromagnetic perturbations of this interacting system is discussed using the linear response theory, and is proved to be fully determined by the physical properties of the intrinsic elementary excitations guided-wave polaritons of the system. The theory is useful for discussions of propagation, transmission, reflection, scattering and absorption of electromagnetic waves as well as the propagation of external electric-, magnetic-or acoustic-perturbations in the planar waveguide.