Sandwiching emissive organic thin films into a planar Fabry-Perot cavity causes quantum electrodynamic effects such ns light intensity enhancement and spectral narrowing to become effective. This enables efficiency-enhanced organic light-emitting diodes to be realized. Recent research activities in this area are summarized and differences in the emission behavior of materials with broad and narrow fluorescence halfwidths are pointed out. Finally, an optimized multilayer structure that underlines the enormous potential of such resonant cavity devices is described.