U.S. Route 1 or U.S. Highway 1 (US 1) is a major north–south United States Numbered Highway that serves the East Coast of the United States. It runs 2,370 miles (3,810 km) from Key West, Florida, north to Fort Kent, Maine, at the Canadian border, making it the longest north–south road in the United States. US 1 is generally paralleled by Interstate 95 (I-95), though US 1 is significantly farther west (inland) between Jacksonville, Florida, and Petersburg, Virginia, while I-95 is closer to the coastline. In contrast, US 1 in Maine is much closer to the coast than I-95, which runs farther inland than US 1. The route connects most of the major cities of the East Coast from the Southeastern United States to New England, including Miami, Jacksonville, Raleigh, Richmond, Washington D.C., Baltimore, Philadelphia, New York City, and Boston.

While US 1 is generally the easternmost of the main north–south U.S. Routes, parts of several others occupy corridors closer to the ocean. When the road system was laid out in the 1920s, US 1 was mostly assigned to the existing Atlantic Highway, which followed the Atlantic Seaboard Fall Line between the Piedmont and the Atlantic Plain north of Augusta, Georgia. At the time, the highways farther east were of lower quality and did not serve the major population centers. From Henderson, North Carolina, to Petersburg, Virginia, it parallels I-85. Construction of the Interstate Highway System gradually changed the use and character of US 1, and I-95 became the major north–south East Coast highway by the late 1960s.