Union is a subway station on Line 1 Yonge–University of the Toronto subway in Toronto, Ontario, Canada. It opened in 1954 as one of twelve original stations on the first phase of the Yonge line, the first rapid transit line in Canada. It was the southern terminus of the line until the opening of the University line in 1963, and is today the inflection point of the U-shaped line. Along with Spadina station and Queens Quay station, it is one of three stations open overnight to support late-night streetcar routes.

Union station is located on Front Street between the Yonge Street and University Avenue sections of the line. It is named for and directly connects to the railway station and regional bus terminal of the same name, serving all GO Transit train lines and train-bus services as well as Via Rail intercity routes (including Amtrak's Maple Leaf service to New York City). It connects to the Union Pearson Express (UPX), a dedicated rail link to Toronto Pearson International Airport. It is the only subway station with a direct connection to Via services.

Based on Toronto's street grid, Union is the southernmost subway station and the closest to Lake Ontario; however, using standard compass directions, Kipling and Islington stations are further south. It serves approximately 100,000 people a day, ranking it as the fourth-busiest station in the system, after Bloor–Yonge, St. George, and Sheppard–Yonge, and the busiest served by only one line. Adjacent to the subway station is an underground terminal loop for the 509 Harbourfront and 510 Spadina streetcar.

In 2007, Union subway station became the first location on the TTC where Presto cards could be used, as part of a trial. Wi-Fi service has been available at this station since 2014.

The station opened as the southern terminus of the original Yonge subway line on March 30, 1954.

On February 28, 1963, Union became a through station with the opening of the University section of the Yonge–University line.

On June 22, 1990, Union became the terminus of route 604 Harbourfront LRT, now part of the 509 Harbourfront and 510 Spadina streetcar routes. A new underground streetcar platform was built south of the subway tracks, connected to the station concourse by a 30-metre pedestrian tunnel and a flight of stairs.

Elevators were installed in 1996, making Union one of the first wheelchair-accessible subway stations in Toronto. An elevator was added to the streetcar platforms, even though streetcars were not accessible themselves. By the time accessible streetcars began serving the station in 2014, the elevator had been replaced as a part of the station expansion.

On August 18, 2014, a second subway platform was opened to serve Yonge line trains, leaving the existing platform to serve only University line trains.

In 2003, planning began on a station expansion to address overcrowding in the station. Despite being one of the busiest stations in the system, the station had only one narrow island platform serving both the University and Yonge lines, and a small concourse area.

The plan was to build a new subway platform on the south side of the tracks to serve the Yonge portion of the line, leaving the existing island platform to serve only the University portion. This new platform would feature a step-free connection to the streetcar platform. The project also included an expansion of the concourse level, the replacement of all finishes and signage, installation of public art, as well as improved connections to the adjacent Union Station and the PATH network.

At a cost of $137 million, construction began in February 2011, with the new second platform opening on August 18, 2014. The project was completed in 2015 with the completion of the station renovation.

In 2019, as part of the rebuilding and expansion of the adjacent Union Station, large glass canopies were installed in the "moat" that connects the subway station to the rest of the Union station complex. This weather-protected route connecting to the main concourses at Union Station ensures that commuters do not need to go outside when entering or leaving the TTC station.

When the station opened in 1954, the wall coverings were glossy yellow Vitrolite tiles with red lettering and trim, and the station name on the walls was in the TTC's unique Toronto Subway Font. During renovations in the 1980s, the yellow Vitrolite tiles were replaced with brown ceramic tiles and vinyl siding, and the station font was changed to Univers.

The 2011 to 2015 station expansion replaced these tiles and panels with white tiles and black trim, and the font used to render the station name was returned to its original Toronto Subway typeface.

As part of the second platform project, a glass wall was built to block off the southern side of the old platform, since it now only serves the University line. It features the art piece "Zones of Immersion" by Stuart Reid, a professor at the OCAD University The work comprises 166 large glass panels, each measuring more than one by two metres, extending 170-metre (560 ft) along the length of the platform. Mostly transparent, it is visible from both the Yonge and University platforms. Each panel contains images or words, many based on sketches that Reid drew while riding the subway. Public reaction towards the art piece has been mixed, with some users of the station finding it "tragic" or "dark and depressing".