The 109th Congress, like the two before it, is expected to consider proposals to control emissions of multiple pollutants from electric power plants. The bills include an Administration-based proposal, the Clear Skies Act (S. 131), which would control emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and mercury, and other bills that would control the three pollutants plus the greenhouse gas carbon dioxide. Much of the debate surrounding the Administration's Clear Skies proposal has focused on its cap-and-trade implementation scheme. But in some ways, the proposal's cap-and-trade provisions are its least significant aspects in terms of the proposal's interaction with the structure of the Clean Air Act. EPA has already promulgated regulations using a regional cap-and-trade program to control NOx emissions over the eastern United States (the "NOx SIP Call") under existing Clean Air Act authority, and has proposed other cap-and-trade regulations to achieve Clear Skies' level of reductions over 28 eastern states and the District of Columbia for both SO2 and NOx (in the Clean Air Interstate Rule). In addition, EPA has proposed capand-trade regulations to achieve mercury reductions similar to those in Clear Skies, although the legality of these regulations is more questionable. Critical to the fabric of the Clean Air Act are the various provisions in Clear Skies to alter or to delete existing sections of the Act with respect to both electric generating units (EGUs) and industrial sources that choose to opt into the program. The Administration has made it clear that with Clear Skies' comprehensive approach to EGUs and opt-ins, it believes certain CAA provisions need no longer apply to them, in some cases permanently, in others for as long as 20 years or under certain conditions. These include most statutory requirements for Prevention of Significant Deterioration and attainment of National Ambient Air Quality Standards under Title I of the Act, as well as most controls on hazardous air pollutants as they apply to EGUs and opt-ins. These changes would diminish the suite of options states currently have to achieve compliance with air quality standards. In July 2001 testimony, then-EPA Administrator Whitman identified the central issue in Clear Skies' interaction with current law: Are the emission reduction targets stringent enough to permit the relaxing or removal of current provisions of the Clean Air Act designed to achieve the same thing with respect to electric utilities? EPA's analysis indicates that Clear Skies will not achieve either the 8-hour ozone or the fine particulate ambient air quality standards that the agency recently implemented within current CAA compliance deadlines. Some nonattainment areas will need additional controls and time to reach attainment. Clear Skies addresses these issues in part by providing 5 to 15 years of additional time, while effectively removing additional electric utility control from the suite of options available to states to achieve the standards. Similarly, with mercury, Clear Skies proposes relatively modest controls on electric utilities, and, as currently drafted, would effectively remove additional electric utility controls from the suite of options available to the states. The ability of industrial sources to opt into Clear Skies could further reduce state control options for both mercury and criteria pollutants. This report will not be updated.