Oregon Route 18 is a state highway that runs between the Oregon Coast, near Lincoln City, and Newberg. OR 18 traverses the Salmon River Highway No. 39 of the Oregon state highway system, named after the river alongside its westernmost segments.

The Salmon River flows from the Central Oregon Coast Range to the Pacific Ocean coast of northwest Oregon in the United States. About 24 miles (39 km) long, it begins and ends in Lincoln County but also flows briefly through western Polk and southern Tillamook counties. Much of its course lies within the Siuslaw National Forest.