Oregon Route 99 is a state highway that runs between the southern border of Oregon, and the city of Junction City. Oregon Route 99 was formed from parts of the former U.S. Route 99; it shares much of its route with I-5, but much of it is also independent. Between Portland and Junction City, the highway is forked into two routes: Oregon Route 99E and Oregon Route 99W.

U.S. Route 99 (US 99) was a main north–south United States Numbered Highway on the West Coast of the United States until 1964, running from Calexico, California, on the Mexican border to Blaine, Washington, on the Canadian border. It was assigned in 1926 and existed until it was replaced for the most part by Interstate 5. Known also as the "Golden State Highway" and "The Main Street of California", US 99 was important throughout much of the 1930s as a route for Dust Bowl immigrant farm workers to traverse the state. Large portions are now California State Route 99 (SR 99), Oregon's Routes 99, 99W, and 99E, and Washington's SR 99. The highway in Washington connected to British Columbia Highway 99, whose number was derived from that of US 99, at the Canada–US border.