Combined heat and power is a highly efficient energy process that produces significantly fewer combustion products per unit of energy output than traditional discrete heat and power generation systems. This, in turn, has a beneficial effect on air pollution and its consequences. Although installing a CHP system usually increases the fuel consumption on-site, the use of cleaner combustion plant often results in a reduction in some of the pollutants produced. By generating electricity on-site, CHP also displaces the larger amounts of fuel otherwise used at central power generating stations, significantly reducing their emissions of pollutants. Included are sections dealing in depth with fossil fuels combustion, conventional energy supply emissions, CHP emissions, CHP emissions reductions, operations & maintenance requirements.