The paper describes the Integrated Air Pollution Control System (IAPCS), a computerized program that can be used to estimate the cost and performance of pre-combustion, in situ, and post-combustion air pollution control configurations in pulverized-coal-fired utility boilers of 100 to 1000 MW. Modular program design and flexible parameter files allow the user to alter the design and cost basis of any control technology, optimize the emission/cost output, and identify least-cost control alternatives. Physical and chemical characteristics of the flue gas are calculated by material balance and reported in an emission-reduction summary. The program tracks changes in gas temperature, pressure, and volume; fly ash and alkalinity; gaseous pollutants and components; moisture content; and reagent recycling. Capital and annual cost estimates are presented in standardized format for easy comparison with other estimates. Control technologies include physical coal cleaning, limestone injection multistage burners (LIMB), low-NOx burners or overfire air ports, spray humidification, dry sorbent injection, dry scrubbing, limestone flue gas desulfurization, electrostatic precipitators, and fabric filters. Integrated combinations of these can be optimized both for existing boilers and for new boilers.