List of Interstate Highways in Washington

Markers for I-5, I-90, and I-405
Map of Washington's highways with the Interstates in red
System information
Length:	764.27 mi (1,229.97 km)
Highway names
Interstates:	Interstate X (I-X)
US Highways:	U.S. Route X (US X)
State:	State Route X (SR X)
System links
State highways in Washington Interstate US State Scenic Former PSH 1964 renumbering Former

In the U.S. state of Washington, there are seven roads that are part of the Interstate Highway System, three primary routes and four auxiliary routes, spanning 764.27 miles (1,229.97 km). These highways connect every city in the state with a population of over 100,000 (Seattle, Spokane, Tacoma, Vancouver, Bellevue, and Everett) as well as the state capital, Olympia.

Interstate 90 (I-90) is the longest primary Interstate Highway in Washington, which connects Seattle to Spokane and the Idaho border, measuring 297.52 mi (478.81 km), while I-82, connecting the Oregon border city of Umatilla to Elensburg via Yakima, is the shortest at 132.57 mi (213.35 km). The longest auxiliary Interstate Highway in Washington is I-405, a bypass of Seattle through the eastside, at 30.30 mi (48.76 km), and the shortest is I-705, a spur into downtown Tacoma, at 1.50 mi (2.41 km). One route, I-605, has been proposed over the years to form another eastside bypass, however there are no plans to construct this fifth auxiliary route.

After passage of the Federal Aid Highway Act of 1956, which formed the Interstate Highway System, the American Association of State Highway Officials had approved I-5 and I-90 across Washington on August 17, 1957. I-82 was approved on October 17, 1957, two months after I-5 and I-90, as part of a 1,102-mile-long (1,773 km) addition to the Interstate Highway System.