A review of progress in thermophotovoltaic generation of electricityfnafnaI began writing this paper immediately after the Third nrel Conference on Thermophotovoltaic Genertion of materials, devices, and systems; substantial gains in fundamental understanding and performance of the quaternary alloy GaInAsSb; the introduction of new radiator concepts; and more attention being paid to modeling of both real and conceptual systems. There was also further evidence of interest in non-military applications, particularly from the European and Japanese attendees.