U.S. Route 101, or U.S. Highway 101 (US 101), is a north–south United States Numbered Highway that traverses the states of California, Oregon, and Washington on the West Coast of the United States. It travels for over 1,500 miles (2,400 km), primarily along the Pacific Ocean, and is also known by various names, including El Camino Real in parts of California, the Oregon Coast Highway, and the Olympic Highway in Washington. Despite its three-digit number, normally used for spur routes, US 101 is classified as a major route in the United States Numbered Highway System.

The United States Numbered Highway System is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these highways were coordinated among the states, they are sometimes called Federal Highways, but the roadways were built and have always been maintained by state or local governments since their initial designation in 1926.