Editors' Summary: The Clean Air Act requires the states and EPA to aggressively attack the problem of air pollution in the nation's cities. The Act's 1977 Amendments directed states to adopt and implement plans, including transportation controls and other measures, to ensure attainment of health standards by 1982 (or in some cases 1987). Despite the statutory mandate, many states have failed to adopt adequate plans, and others have failed to implement the plans that have been adopted. With dozens of cities still in nonattainment, citizens groups are increasingly asking the courts to impose sanctions on delinquent areas, to order implementation of adopted plans, and to force EPA to impose federal controls to ensure attainment. This Article describes the legal framework for urban air quality litigation under the Act and analyzes the issues presented in these cases.