The U.S. Supreme Court in Massachusetts v. EPA held that carbon dioxide is a pollutant under the Clean Air Act (CAA) and remanded the case to EPA. The Agency must decide whether CO2 emissions contribute to climate change. If the Agency responds affirmatively, it must meet other requirements of the CAA in order to regulate carbon dioxide or other greenhouse gases (GHGs). This Article explains why the CAA is a poor vehicle for regulating GHGs and covers in detail the difficulties that will arise in trying to use the Act to reduce CO2 emissions. The Article then turns to what should be done to develop an energy policy that will effectively reduce U.S. GHG emissions. It examines the options for control, including the use of taxes and cap-and-trade programs and evaluates some of the most important legislative proposals being considered. It then turns to the two major sources of GHGs—electric power production and motor vehicle use—and addresses how the adverse impact these sources have on our climate could be reduced.