U.S. Route 30 or U.S. Highway 30 (US 30) is an east–west main route of the United States Numbered Highway System, with the highway traveling across the Northern U.S. With a length of 3,072 miles (4,944 km), it is the third-longest U.S. Highway, after US 20 and US 6. The western end of the highway is at US 101 in Astoria, Oregon; the eastern end is at Virginia Avenue, Absecon Boulevard, and Adriatic Avenue in Atlantic City, New Jersey. The "0" as the last digit in the number indicates that it is a coast-to-coast route and a major east–west route. Despite long stretches of parallel and concurrent Interstate Highways, it has not been decommissioned unlike other long-haul routes such as US 66. It is also the only U.S. Highway that has always been coast-to-coast since the beginning of U.S. 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.