A quantum theory of the coupling of excited molecules to the surface plasmon modes of a metal is described. For radiative decay, formulas are given for the separate decay into s photon, p photon and surface plasmon channels valid for all molecule-metal separations. Calculations of the quantum yield of fluorescence are described. The total decay rate is shown to equal that given by classical theory. Other processes considered briefly are the Raman effect and resonance energy transfer between identical molecules. Copyright © 1975 American Institute of Physics.