By Jonathan S. Martel and Christopher A. Jaros (February 2011; 8 pages) In December 2009, the Environmental Protection Agency issued a final endangerment finding that greenhouse gas emissions from motor vehicles contribute to air pollution, endangering public health and welfare. The finding triggered a series of regulations aimed at reducing greenhouse gas emissions. Also in 2009, EPA said it planned to complete a review by the end of 2011 of the national ambient air quality standards for the six major air pollutants. The authors review the major developments in Clean Air Act regulations and litigation over the past year, outlining how the different rules fit together and what to anticipate as implementation of the Clean Air Act continues.