Homer M. Hadley Memorial Bridge, Road bridge across Lake Washington in Seattle, United States.

The Homer M. Hadley Memorial Bridge is a floating bridge on Lake Washington between Mercer Island and Seattle, carrying the westbound lanes of Interstate 90 and two tracks of the 2 Line light rail. Its 5,811-foot (1,772 m) length makes it the fifth-longest floating bridge in the world. The bridge consists of 18 pontoons, each 105 feet (32 m) wide including cantilevered sections, and a bicycle and pedestrian path on the north side.

The bridge opened on June 4, 1989, completing a critical Interstate 90 segment connecting the two cities. This project significantly improved regional transportation links that had previously been less direct.

The bridge honours Homer More Hadley, the engineer who designed the parallel Lacey V. Murrow Memorial Bridge; it was given his name in 1993. Locals rarely use the official name, calling the pair simply the Mercer Island Bridge or distinguishing between the "new" and "old" bridge, though that is ambiguous because the older span was rebuilt after the Hadley opened.

The bridge carries four westbound lanes of Interstate 90, including an HOV lane, plus two Link light rail tracks on the south side. A 9-foot-wide pedestrian and bicycle path runs along the north side, separated from traffic by a 35-inch concrete barrier and a 54-inch outer railing. Sound Transit monitors wind and waves on Lake Washington and can suspend train service when swells reach certain heights.

The 2 Line, opened on March 28, 2026, made this the first permanent electrified railroad on a floating bridge, following the Maxau pontoon bridge of 1865. Sound Transit monitors wind and waves and can suspend trains when swells reach set heights. The bridge's 18 pontoons were built in Everett and Tacoma and widened with cantilevered sections because of the narrow Ballard Locks.