Resonant energy transfer by dipolar coupling is generally regarded as occurring through two distinct mechanisms. One mechanism is radiative transfer, in which a photon is emitted by the donor molecule and is subsequently absorbed by an acceptor species. The other mechanism is mediated by a radiationless Coulombic intermolecular interaction. Whilst both the radiative and radiationless mechanisms require an overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor, distinctions are usually drawn between other mechanistic features. However, by developing a fully quantum electrodynamical treatment of the radiationless process, it can be shown that Förster's result arises as the short-range limit of a more general dipoledipole interaction based on virtual photon coupling. At large separations R, retardation effects modify the form of the usual R−6 distance dependence to R−2, and the result can be identified with the classical result for radiative transfer. Hence the radiative and radiationless mechanisms for energy transfer must be regarded as indistinguishable.