Editor's Summary: Last year saw many exciting developments in CAA law and policy, including implications and fallout from the U.S. Supreme Court decision in Massachusetts v. EPA. In this Article, Ari G. Altman and Jessica M. Lewis look at a number of cases involving carbon dioxide emissions from both mobile and stationary sources. They address the momentum toward passing climate change legislation in Congress and moving to implement cap-andtrade systems at the regional level, as well as several potential options for regulating greenhouse gases under the existing CAA. Further, they examine a pivotal decision related to the ozone air quality standard, as well as key cases and EPA rulemakings relating to the control of hazardous air pollutants. A recent decision overturning the Clean Air Mercury Rule receives special attention. Finally, they highlight developments in new source review policy and provide a forecast of certain upcoming EPA rulemakings under the CAA.