Union Station is a major railway station and intermodal transportation hub in Toronto, Ontario, Canada. The station is located in downtown Toronto, on Front Street West, on the south side of the block bounded by Bay Street and York Street. The municipal government of Toronto owns the station building while the provincial transit agency Metrolinx owns the train shed and trackage. It is operated by the Toronto Terminals Railway, a joint venture of the Canadian National Railway and Canadian Pacific Railway, which directs and controls train movement along the Union Station Rail Corridor, the largest and busiest rail corridor in Canada. Constructed in 1927, Union Station has been a National Historic Site of Canada since 1975, and a Heritage Railway Station since 1989.

A May 2026 survey by AllClear considered 43 major train stations around the world; the Toronto site placed fifth among the "most luxurious and high-performing rail hubs", the only one in Canada among the top 20.

Its central position in Canada's busiest inter-city rail service area, "The Corridor", as well as being the central hub of GO Transit's commuter rail service, makes Union Station Canada's busiest transportation facility and the second-busiest railway station in North America (behind New York Penn Station), serving over 72 million passengers each year. More than half of all Canadian inter-city passengers and 91 percent of Toronto commuter train passengers travel through Union Station.

Via Rail and Amtrak provide inter-city train services while GO Transit operates regional rail services. The station is also connected to the subway and streetcar system of the Toronto Transit Commission (TTC) at its adjacent namesake subway station. GO Transit's Union Station Bus Terminal, located in CIBC Square, is connected to Union Station by a 40-metre (130 ft) enclosed walkway above Bay Street. The Union Pearson Express, which provides train service to Toronto Pearson International Airport, has a platform a short walk west of the main station building, accessible by the SkyWalk.

Toronto's Union Station is located at 61 Front Street West, between Bay and York Streets in Toronto's business district, with Toronto's Entertainment District beginning across Bay Street. It is roughly at the city's east-west centre. It is also close to Lake Ontario, which marks Toronto's southern boundary. The southernmost part of the Gardiner Expressway, which lies between Union Station and Lake Ontario, provides easy core access to GO Transit buses. Union Station's columned façade and main entrance faces north, towards downtown Toronto. The Fairmont Royal York Hotel, a former railway hotel, is directly across Front Street from Union Station and can be accessed from the station both at street level and via an underground passageway called Path. The Dominion Public Building, another building from the same era, is just to the east of the station, at the corner of Front and Bay Streets.

Other major buildings near Union Station are Telus Tower, Royal Bank Plaza, and Brookfield Place. Brookfield Place is home to the Allen Lambert Galleria, a six story high pedestrian thoroughfare, as well as the Hockey Hall of Fame, which holds the Stanley Cup.

Scotiabank Arena, Rogers Centre, Metro Toronto Convention Centre, and the CN Tower are all close by, and are visible from some parts of the station. Like Union Station, these structures were built on former Railway Lands. All of them can be accessed directly from Union Station via the Skywalk. The land around the CN Tower has been converted to a public park. Union Station will soon be linked via a Path bridge on the east side to the Backstage Condominium building at the corner of Esplanade and Yonge Street.

Toronto's Union Station is Canada's largest and most opulent railway station. The Montreal architecture firm of Ross and Macdonald designed the building in the Beaux-Arts style as a joint venture between the Grand Trunk Railway and the Canadian Pacific Railway, with help from CPR architect Hugh Jones and Toronto architect John M. Lyle. In 1975, the Historic Sites and Monuments Board of Canada cited its design as being of "national architectural significance as one of the finest examples of Beaux-Arts railway station design in Canada".