Sound Transit (ST), officially the Central Puget Sound Regional Transit Authority, is a public transit agency serving the Seattle metropolitan area in the U.S. state of Washington. It operates the Link light rail system in Seattle and Tacoma, regional Sounder commuter rail, and Sound Transit Express bus service. The agency also coordinates the regional ORCA fare card system, which is also used by local transit operators. In 2019, Sound Transit services carried a total of 48 million passengers and averaged over 161,000 riders on weekdays.

Link light rail is a light rail rapid transit system serving the Seattle metropolitan area in the U.S. state of Washington. It is managed by Sound Transit in partnership with local transit providers, and consists of three non-connected lines: the 1 Line in King County, which travels for 26 miles (42 km) between Seattle and Seattle–Tacoma International Airport; the 2 Line in King County's Eastside region between Bellevue and Redmond; and the T Line in Pierce County, which runs for 4 miles (6.4 km) between Downtown Tacoma and Tacoma Dome Station. In 2023, the system had a ridership of 23.9 million, or about 78,600 per weekday as of the fourth quarter of 2023, primarily on the 1 Line. Trains run at frequencies of 6 to 24 minutes.