Interstate 405 (I-405) is a north–south auxiliary Interstate Highway serving the Seattle region of Washington, United States. It bypasses Seattle east of Lake Washington, traveling through the Eastside area of King and Snohomish counties, providing an alternate route to I-5. The 30-mile (48 km) freeway serves the cities of Renton, Bellevue, Kirkland, and Bothell. I-405 terminates at I-5 in Tukwila and Lynnwood, and also intersects several major highways, including SR 167, I-90, SR 520, and SR 522.

The Eastside of the King County, Washington area in the United States is a collective term for the suburbs of Seattle located on the east side of Lake Washington.