The Clean Air Act (CAA) is the United States' primary federal legislation designed to control air pollution on a national level. It was first enacted on December 17, 1963, as the Clean Air Act of 1963 (Pub. L. 88–206), marking the first time the federal government was granted authority to directly regulate air quality, building on earlier efforts like the Air Pollution Control Act of 1955. The Act was significantly amended in 1970, establishing the modern framework that empowers the Environmental Protection Agency (EPA), created that same year, to set and enforce national ambient air quality standards, regulate emissions from stationary and mobile sources, and address hazardous air pollutants. Further amendments in 1977 and 1990 strengthened provisions for acid rain control, ozone layer protection, and market-based approaches like emissions trading, including a cap-and-trade system for acid rain pollutants, leading to substantial reductions in pollutants such as lead, sulfur dioxide, and particulate matter over the decades.

The CAA has been instrumental in improving public health and environmental quality, preventing an estimated 230,000 premature deaths annually by 2020 and reducing instances of asthma, heart disease, and respiratory illnesses. It requires states to develop implementation plans to meet federal standards and allows the EPA to intervene in non-attainment areas. However, the law has faced ongoing controversies, including rollbacks under various administrations; for instance, in 2025, protections against hazardous air pollutants were reportedly abolished, releasing over 1,000 industrial polluters from emission reduction requirements. Recent legislative efforts, such as bills introduced in Congress to reform sections addressing wildfires, exceptional events, and permits for critical industries like rocket engines and advanced manufacturing, highlight ongoing debates over balancing environmental protection with economic and national security interests.

Enforced primarily through the EPA, the CAA operates within the framework of U.S. federal government, with headquarters effectively in Washington, D.C. It has influenced global environmental policy and remains a cornerstone of U.S. efforts to combat climate change and air toxics, though criticisms persist regarding enforcement inconsistencies, industry exemptions, and political interventions, such as those affecting lead pollution sources or power sector regulations.