The hours of service (HOS) are regulations issued by the Federal Motor Carrier Safety Administration (FMCSA) governing the working hours of anyone operating a commercial motor vehicle (CMV) in the United States for the purpose of "interstate commerce"— moving commercial goods from one U.S. state to another. This includes truck drivers and bus drivers who operate CMVs for motor carriers (their employers). These rules limit the number of daily and weekly hours spent driving and working, and regulate the minimum amount of time drivers must spend resting between driving shifts. For intrastate commerce, the respective state's regulations apply.

The FMCSA is a division of the United States Department of Transportation (DOT), which is generally responsible for enforcement of FMCSA regulations. The driver of a CMV is required to keep a record of working hours using a log book, outlining the total number of hours spent driving and resting, as well as the time at which the change of duty status occurred. In lieu of a log book, a motor carrier may keep track of a driver's hours using an electronic on-board recorder (EOBR), which automatically records the amount of time spent driving the vehicle.