The state-of-the-art of the theory and control of NO/sub x/ emissions from combustors is reviewed including the mechanisms and kinetics of the formation of thermal and fuel NO/sub x/, its destruction by reactions with char and reducing gases, and NO/sub x/ emissions control technology and mathematical modeling of fluidized-bed combustors. Practical conclusions are drawn, some unsolved problems are described, and recommendations are made as to various topics which require further study.