The chapter discusses the use of technologies for reducing air pollution emissions from stationary sources, with emphasis on the control of combustion generated air pollution. Major stationary sources include utility power boilers, industrial boilers and heaters, metal smelting and processing plants, and chemical and other manufacturing plants. The three primary approaches are pre-process control, process modification, and post-process control. Early work in the field of air pollution technology focused on sulfur dioxide, nitrogen oxides, and particulates. Work continues to improve performance as measured by pollutant reduction efficiency and operating and maintenance cost. These mature technologies are also being evlauated for their performance as control devices for hazardous air pollutants, and as the basis for new hybrid technologies that seek to reduce pollutant emissions by 90% or more.