Theoretical bases of combustion process modifications aimed at the reduction of pollutant emission are examined. It is shown, as an example, of how the minimization of emissions of nitrogen oxides leads to a design protocol that translates results of modeling and of bench scale experiments into guidelines for industrial design. The formation and emission of polycyclic aromatic compounds is also considered, because their formation is strongly favored in ＇＇low NOx flames＇＇. In power generation the pollutant emission can be reduced effectively by the improvement of the ＇＇heat rate,＇＇ i.e., the thermodynamic efficiency of the power cycle. Combined gas turbine-steam cycles which have strong potential for high thermal efficiency may, however, present new challenges to combustion research. Technology responses to such problems are discussed.