The report gives results of an environmental assessment of combustion modification techniques for coal-, oil-, and gas-fired industrial boilers, with respect to NOx control reduction effectiveness, operational impact, thermal efficiency impact, capital and annualized operating costs, and effect on emissions of pollutaants other than NOx. Major industrial boiler design types and equipment trends are reviewed. Currently available control techniques can reduce NOx 10-25% for coal- and residual-oil-fired boilers, and 40-70% for distillate-oil- and gas-fired units with minimal adverse operating impacts. Controls should increase steam costs by only 1-2%, but the initial investment required could be significant, up to 20% on a new boiler and easily up to 40% on a retrofit. Detailed Level 1 tests on two stoker-coal-fired boilers indicate that combustion modification reduces the potential environmental hazard of the source by lowering NOx emissions, without significant effect on the emissions of other pollutants.