State Route 520 (SR 520) is a state highway and freeway in the Seattle metropolitan area, part of the U.S. state of Washington. It runs 13 miles (21 km) from Seattle in the west to Redmond in the east. SR 520, a major regional freeway, connects Seattle to the Eastside region of King County via the Evergreen Point Floating Bridge, which crosses Lake Washington. SR 520 intersects several state highways, including Interstate 5 (I-5) in Seattle, Interstate 405 (I-405) in Bellevue, and SR 202 in Redmond.

The original Evergreen Point Floating Bridge was opened in 1963 as a replacement for the cross-lake ferry system that had operated since the turn of the century. SR 520 was designated in 1964 as a freeway connecting I-5 to I-405, while an extension to Redmond was proposed later in the decade. In the 1970s and 1980s, sections of the freeway between Bellevue and Redmond were opened to traffic, replacing the temporary designation of State Route 920 (SR 920).

Since the 1990s, SR 520 has been expanded with high-occupancy vehicle lanes (HOV lanes) and new interchanges to serve the Overlake area. The original Evergreen Point Floating Bridge was replaced in 2016 by a wider bridge, as part of a multi-billion dollar expansion program that is scheduled to be completed in the 2020s. The program also includes the construction of new bus infrastructure at Montlake and on the Eastside, as well as a bicycle and pedestrian path along most of the highway's length.