U.S. regulations
Pollutant emissions of combustion engines

U.S. federal regulations are set by the Environmental Protection Agency (EPA). The development of engine emission standards follows the procedures of the U.S. regulatory process. New regulations are first published as proposals. After a period of public debate, they are signed into law. New standardization proposals are published in the Federal Register. Consolidated regulations become part of the Code of Federal Regulations (CFR).

The State of California has the right to adopt its own emissions regulations, which are often more stringent than federal rules. They are adopted by the California Air Resources Board (CARB), a California EPA standards body. It is the only state to develop its own regulations. Other states can choose between federal and California regulations.