U.S. Route 18 (US 18) is an east-west U.S. Numbered Highway in the state of Wyoming. It extends approximately from Interstate 25 (I-25) at Orin to the South Dakota state line east of Mule Creek Junction. US 18 continues east to its terminus in Milwaukee, Wisconsin.
US 18 begins in Orin concurrent with US 20 at I-25 (itself concurrent with US 20, US 26, and US 87) and travels east to Lusk, where US 18 branches off to run concurrently with US 85 for . At the unincorporated community of Mule Creek Junction in northeastern Niobrara County, US 18 leaves US 85. This stretch from US 85 to the South Dakota border is the only segment of US 18 in Wyoming which is not cosigned with another highway. Running for nearly , US 18 has a speed limit of with the exception of its ending terminus at Orin and the portion throughout Lusk.