Whether U.S. EPA and states can regulate emissions outside the facility fence line is a critical factor in shaping the regulatory response to climate change using Clean Air Act §111. There has been much rhetoric about the ability of states and EPA to create regulatory tools such as emissions trading of greenhouse gases, but policy experts and professionals need a more definitive answer. To address this topic, ELI held the second seminar of its Professional Practice Series. Loosely following an academic debate structure, two expert teams argued the resolution, asked questions of the other side, and identified points of agreement and disagreement. Following the debate, the discussion was open to audience questions.