The Mount Baker Tunnel or Mount Baker Ridge Tunnel carries Interstate 90 under the Mount Baker neighborhood of Seattle, Washington. It is actually a group of three tubes (or four --if counting the two original Mount Baker Tunnels separately) that carry eight lanes of freeway traffic, plus a separate path for bicycles and pedestrians. The original tubes are twin tunnel bores completed in 1940 and rehabilitated in 1993. The new Mount Baker Tunnel was built north of the original tunnels and opened in June 1989. The tunnel has a double-decked roadway with the bicycle/pedestrian path above the traffic lanes.

The tunnel was listed on the National Register of Historic Places in 1982 (ID #82004243). The east portals of the tunnel, with murals titled Portal of the North Pacific designed by artist James FitzGerald, along with the Lacey V. Murrow Bridge, are an official City of Seattle landmark.

The official length is 1,440 feet (440 m), though the perceived length while driving is closer to 3,300 feet (1,000 m) because of a cut-and-cover "lid" between the western portal and the beginning of the actual tunnel under the Mount Baker ridge. The former west portal, now located well inside the tunnel, is no longer discernible and its two arch structures were removed during 1989–1993 modification work. The eastern end of the tunnel links to the Lacey V. Murrow Memorial Bridge and the Homer M. Hadley Memorial Bridge (collectively the I-90 floating bridge) on Lake Washington, to Mercer Island.

At 63 feet (19 m) in diameter, it is the world's largest diameter soft earth tunnel, having been bored through clay.