U.S. Route 18 (US 18) is an east–west U.S. highway in the Midwestern United States. The western terminus is in Orin, Wyoming at an interchange with Interstate 25. Its eastern terminus of US 18 is in downtown Milwaukee, Wisconsin. However, US 18 runs concurrent with other U.S. routes from its western terminus to Mule Creek Junction, Wyoming.

US 18 is one of the original United States highways of 1926. The US 18 designation was originally proposed for a road in Michigan from Grand Haven east to Detroit. This roadway was eventually designated as U.S. Route 16.