The National Highway Traffic Safety Administration (NHTSA NITS-ə) is an agency of the U.S. federal government, part of the Department of Transportation. It describes its mission as "Save lives, prevent injuries, reduce vehicle-related crashes" related to transportation safety in the United States.

NHTSA is charged with writing and enforcing Federal Motor Vehicle Safety Standards as well as regulations for motor vehicle theft resistance and fuel economy, as part of the Corporate Average Fuel Economy (CAFE) system. FMVSS 209 was the first standard to become effective on March 1, 1967. NHTSA licenses vehicle manufacturers and importers, allows or blocks the import of vehicles and safety-regulated vehicle parts, administers the vehicle identification number (VIN) system, develops the anthropomorphic dummies used in U.S. safety testing as well as the test protocols themselves, and provides vehicle insurance cost information. The agency has asserted preemptive regulatory authority over greenhouse gas emissions, but this has been disputed by such state regulatory agencies as the California Air Resources Board.

The Federal Motor Vehicle Safety Standards are contained in the United States 49 CFR 571. Additional federal vehicle standards are contained elsewhere in the CFR. Another of NHTSA's major activities is the creation and maintenance of the data files maintained by the National Center for Statistics and Analysis. In particular, the Fatality Analysis Reporting System (FARS), has become a resource for traffic safety research not only in the United States, but throughout the world. Research contributions using FARS by researchers from many countries appear in many non-U.S. technical publications, and provide a significant database and knowledge bank on the subject. Even with this database, conclusive analysis of crash causes often remains difficult and controversial, with experts debating the veracity and statistical validity of results.