The paper is a brief discussion and summary of state-of-the-art combustion modification NOx control technology for boilers and industrial process combustion equipment. These combustion modification techniques, when properly applied, offer the potential for cost-effective NOx control for the major fossil-fuel-fired stationary combustion sources in the near term. NOx, principally NO and NO2, are atmospheric pollutants with potential for adverse effects on human health and welfare. Fuel combustion contributes about 99% of technology-related NOx emissions. Because of human activities in urban areas, NOx concentrations are frequently 10 to 100 times higher there than in nonurban areas. NOx enters into complex atmospheric photochemical reactions in the presence of hydrocarbons and results in the formation of undesirable secondary species. Also, recent studies indicate that NOx contributes to the formation of acid precipitation. The effects of NO2 were among the factors leading to the passage in the U.S. of the 1970 Clean Air Act and succeeding amendments which require the control of pollutant emissions to protect human health and welfare. The U.S. EPA has established regulatory standards for NOx, as well as for other pollutants, from a range of sources. These regulations have prompted efforts to identify and evaluate the performance of effective controls for NOx emissions.