The National Highway Traffic Safety Administration (NHTSA, pronounced "NITZ-ah")[7] 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"[8] related to Transportation safety in the United States.

As part of its activities, 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 1 March 1967. NHTSA also 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 Code of Federal Regulations, Title 49, Part 571. This is commonly referred to as 49CFR571, with any particular FMVSS appended after a period; for example 49CFR571.301 is the location of FMVSS 301. Additional federal vehicle standards are contained elsewhere in the CFR. For instance, 49CFR564 contained the specifications and requirements for various types of replaceable headlamp light sources (bulbs), until this information was moved to a docket elsewhere, with effect from 2 December 2012.[9]

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,[10] 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.[10]