The United States and China are the top two energy consumers in the world. As a consequence, they are also the top two emitters of numerous air pollutants which have local, regional, and global impacts. Urbanization has led to serious air pollution problems in U.S. and Chinese cities; although U.S. cities continues to face challenges, the lessons they have learned in managing energy use and air quality are relevant to the Chinese experience. This book summarizes current trends, profiles two U.S. and two Chinese cities, and recommends key actions to enable each country to continue to improve urban air quality.