Pioneer Square station is a light rail station that is part of the Downtown Seattle Transit Tunnel in Seattle, Washington, United States. The station is located under 3rd Avenue at James Street, between Symphony and International District/Chinatown stations. It is served by the 1 Line, part of Sound Transit's Link light rail system, and provides connections to local buses and Colman Dock, a major ferry terminal serving areas west of Seattle.

The station consists of two side platforms situated under street level, with two mezzanines connecting to the surface at James Street and Yesler Way in Seattle's Pioneer Square neighborhood. It opened on September 15, 1990, and was used exclusively by buses until 2009. The tunnel and stations closed for almost two years, from 2005 to 2007, for renovation and modifications to accommodate light rail trains. Link light rail service to Pioneer Square station began on July 18, 2009, and bus service ended on March 23, 2019. Trains serve the station twenty hours a day on most days at a frequency of six minutes during peak periods and 12–20 minutes at other times. In early 2020, Pioneer Square station served as a transfer point between trains with a temporary center platform as part of construction for the 2 Line.

Pioneer Square station is located under 3rd Avenue between Cherry Street and Yesler Way in the Pioneer Square neighborhood of Downtown Seattle. The station is at the northern end of the Pioneer Square National Historic District, where the city's oldest buildings are located, and is near the Seattle Underground Tour and the Klondike Gold Rush National Historical Park. To the north and east is the Seattle Civic Center, a complex of city and King County government office buildings, including Seattle City Hall and the King County Courthouse. Pioneer Square station is six blocks east of Colman Dock, the city's primary ferry terminal for Washington State Ferries and King County Water Taxi service.

Much of the non-government and non-historic land use around Pioneer Square station is for high-rise offices and multi-family housing. Within a 1⁄2-mile (0.8 km) radius of the station is an estimated population of 12,866 people, and approximately 69,795 jobs. Nearby office towers include Smith Tower, the Columbia Center, and Wells Fargo Center. The corporate headquarters of logging company Weyerhaeuser was moved from Federal Way to Occidental Park near Pioneer Square station in 2016; the company cited transit access as one of its main reasons to choose the neighborhood.

Pioneer Square was developed as Seattle's initial settlement in the 1850s and continued to serve as the city's downtown into the early 20th century. In 1911, civil engineer Virgil Bogue presented a comprehensive plan for the city of Seattle, including a rapid transit system centered around a "trunk" subway under 3rd Avenue, passing through Pioneer Square and the growing commercial and retail district to the north. The plan was rejected by voters on March 5, 1912, and the 3rd Avenue subway was unsuccessfully proposed twice in the 1920s.

In the late 1960s, the Forward Thrust Committee put forward a ballot measure to fund a rapid transit system in the Seattle metropolitan area, including a downtown subway under 3rd Avenue with a station between Cherry and James streets. The ballot measure, requiring a supermajority to support bonding to augment $385 million in local funding with $765 million from the Urban Mass Transportation Administration, failed to reach the 60 percent threshold in 1968 and again during a second vote in 1970. The failure of the Forward Thrust ballot measures led to the creation of Metro Transit in 1972, operating bus service across King County.

Metro Transit began planning a bus tunnel through downtown Seattle in the 1970s, to be eventually converted to use by light rail trains. Metro approved the construction of a bus tunnel under 3rd Avenue in 1983, and chose to site one of the tunnel's five stations near the King County Courthouse at 3rd Avenue and James Street. The station was to be completed by late 1989 and use brick, stone, and tile to complement the design of nearby Pioneer Square.

Metro awarded a $44.1 million contract to a joint venture of Atkinson and Dillingham companies to build the tunnel's 3rd Avenue segment as well as Pioneer Square station. Excavation of the station from street level began in March 1987, and the project's twin tunnel boring machines reached James Street from Union Station in September. In June 1987, Atkinson-Dillingham and Metro were fined $80,000 after drilling at the station severed three electric power transmission lines, causing a day-long power outage in downtown Seattle, affecting the City Hall and Public Safety Building. Work in the tunnel station was also blamed for shaking in the City Hall and Public Safety Building, requiring monitoring equipment to be set up by Metro.