Except for New Hampshire, all states and the District of Columbia require adult front-seat occupants of motor vehicles to use seat belts. Adult rear-seat passengers are also covered by the laws in 31 states and the District of Columbia. Children are covered by separate laws.

State seat belt laws are divided into two categories: primary and secondary. Primary seat belt laws allow law enforcement officers to stop a motor vehicle and to issue a ticket or citation to a driver or passenger for not wearing a seat belt without any other traffic offense having occurred. Secondary seat belt laws only allow law enforcement officers to issue a ticket or citation for not wearing a seat belt when there has been another traffic offense by an occupant of the vehicle for which the occupant may be issued a ticket or citation.

In Washington (WA) state, seat belt use is mandated by law under the Revised Code of Washington (RCW) 46.61.688, which is a primary enforcement law. This means that law enforcement officers can stop a vehicle and issue a citation to the driver if the driver or any front-seat passenger is not wearing a seat belt, without needing to have another reason for the traffic stop. Additionally, this law requires all occupants of a vehicle, regardless of where they are seated, to be properly restrained. Washington's law extends to all vehicles that are equipped with seat belts. The state also has specific laws for child restraint; children under the age of 13 are required to ride in the back seat where it is practical to do so, and children up to the age of 8, unless they are 4'9" tall, must be secured in a child restraint system (RCW 46.61.687). Violation of these laws can result in fines and penalties.