The paper describes U.S. research efforts, demonstration projects, and commercial applications designed to control nitrogen oxide (NOx) emissions from stationary sources. Research and development of NOx control techniques in the U.S. has included a variety of combustion-related techniques, as well as selective catalytic reduction (SCR) of NOx with ammonia (NH3). Current U.S. emission standards for both utility and industrial boilers will require either low NOx burners or combustion modifications to achieve compliance. The State of California has more stringent regulations that, in some cases, require the use of SCR to achieve compliance; however, there have been no commercial applications to utility boilers. Results from pilot unit testing of SCR have allowed the costs of full scale systems to be estimated. Current research is directed toward processes that remove NOx and sulfur oxides (SOx) simultaneously.