EPA's legal authority to regulate greenhouse gas emissions under the Clean Air Act is reviewed. While EPA clearly does not have the authority to implement the precise terms of the Kyoto Protocol, arguments could be put forward to support the Agency's claim that it has the authority to control such pollutants. However, the Clean Air Act's legislative history, a textual analysis of the Act, judicial precedents and political considerations all provide compelling arguments for the EPA to seek additional legislation before attempting to regulate greenhouse gases. Even a generous interpretation of existing provisions would prohibit trading in greenhouse gas emissions permits and therefore contradicts the Administration's own preferred approach to addressing climate change which favors employing market mechanisms to help reduce the costs of carrying out reductions. Moreover, the participation of developing countries in an emissions control regime, which has been stipulated by the Senate and endorsed by the Administration, would also remain unaffected since the Clean Air Act is only designed to address local and regional pollution. Concerns over backdoor implementation of the Kyoto Protocol and EPA's attempts to regulate emissions help explain the political attacks on the agency's efforts to pursue research, education, and non-regulatory solutions to the climate change problem.Includes bibliographical references.Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/)