Mercury is a hazardous air pollutant (HAP) that circulates around the globe for a year before depositing back to earth. Mercury emissions from electric power generation sources were estimated by the U.S. Environmental Protection Agency (EPA) to be 48 t/yr, constituting the single largest anthropogenic source of mercury in the United States.1 Controlling mercury emissions from coal-fired power plants is currently the subject of intense legislative and regulatory debate. 2,3 In December 2000, EPA4 determined that regulation of HAP emissions from coal- and oil-fired power plants was “appropriate and necessary” to protect public health, and mercury was deemed to be the HAP of most concern. That determination triggered a rule-making process under which EPA is expected to issue a proposed rule by December 2003 requiring Maximum Achievable Control Technology (MACT) standards. The rule is scheduled to be finalized by December 2004 and power plants would have to comply with the chosen MACT standards by December 2007. Currently, there are no commercial technologies available that can be retrofitted at existing power plants for controlling mercury emissions, although devices to control other pollutants also control some mercury. This month’s EM presents four articles5-8 that focus on the various technologies under development to control mercury emissions from coal-fired power plants.