U.S. Route 30 or U.S. Highway 30 (US 30) is an east–west main route in the system of the United States Numbered Highways, with the highway traveling across the northern tier of the country. With a length of 3,073 miles (4,946 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. Despite long stretches of parallel and concurrent Interstate Highways, it has not been decommissioned unlike other long haul routes such as US 66.

The "0" as the last number in the digit indicates that it is a coast-to-coast route and a major east-west route. Much of the historic Lincoln Highway, the first road across the United States (from New York City to San Francisco), became part of US 30; it is still known by that name in many areas.

US 30 and US 20 break the general U.S. Route numbering guidelines in Oregon, since US 20 actually starts south of US 30 in Newport, Oregon and US 30 runs parallel to the north throughout the state (the Columbia River and Interstate 84). The two run concurrently and continue in the correct positioning near Caldwell, Idaho. This is because US 20 was not a planned coast-to-coast route while US 30 was. US 20 originally ended at the eastern entrance of Yellowstone National Park; it was extended to Albany, Oregon in 1940, then again to Newport in 1943.