Bay is a subway station on Line 2 Bloor–Danforth in Toronto, Ontario, Canada. It is located in the heart of the Yorkville district just north of Bloor Street West on the west side of Bay Street.

The Toronto Transit Commission (TTC) operates its lost articles office at this station, where forgotten objects on the city's buses and trains are held until reclaimed or sold by auction. Wi-Fi service is available at this station.

Bay station opened in 1966 as part of the original segment of the Bloor–Danforth line, from Keele in the west to Woodbine in the east. Early plans of the line, and even some published maps, named this station "Yorkville"; the platform signs read "BAY" in large type, with a smaller "YORKVILLE" caption underneath. Work commenced in August 2019 to make Bay station wheelchair accessible; this work was completed on December 30, 2020.

Below the main platform for Bay station is an abandoned platform, which was used for only six months in 1966 when the TTC experimentally ran trains whose routes included portions of both the Yonge–University and Bloor–Danforth lines. This abandoned platform is sometimes referred to as "Lower Bay" by the general public or "Bay Lower" by the TTC.

The platform was in service from February to September 1966 as part of an interlining experiment, in which the TTC ran trains along three routes, with one matching the subsequent Bloor–Danforth line, and the other two combining parts of the Bloor–Danforth line with the Yonge–University line. The experiment was deemed a failure, largely because delays anywhere quickly cascaded to affect the entire system. Also, as the stations had not been laid out effectively for cross-platform interchange, trains travelling east from St. George and west from Yonge alternated between the two levels, leading passengers to wait on the stairs in-between the levels, since they were unable to tell which platform would receive the next train.

With every station served by at least two routes (Bloor–Yonge station was served by all three routes, with the Yonge–University–Danforth route passing through it twice, once on each level), passengers could travel between any two stations without changing trains; though for some station combinations, such as travel between a station north of Bloor and one on the Bloor–Danforth route, transferring at Bloor–Yonge station resulted in a more direct path. The TTC found that when the extra time waiting for a train from the correct route was considered, the time savings were not significant.

Much of the infrastructure for interlining is still present on the system, and most older stations still have signs informing passengers of each train's next destination, although they no longer change. While St. George and Bloor–Yonge stations remained operating upper and lower platforms for the two crossing subway lines, Bay station would be served by only the Bloor–Danforth line.

Lower Bay and the tracks leading to it still exist and are now used to train new operators, to move trains between the two current lines, for platform-surface experiments, and to allow filming in the subway without disrupting public service. The station has been modified several times to make it look like a "common" North American subway station, and the TTC once had an elaborate pre-built set for converting it to a New York subway station. The set was used for the filming of the movie Don't Say a Word. The TTC asked the production company if they could donate the set. The set remained up for about three weeks as a selling point for other movies but was then torn down due to safety concerns. Other notable movies shot at Lower Bay include The Taking of Pelham One Two Three, Johnny Mnemonic, Bulletproof Monk, Mimic, End of the Line, The Recruit, and most recently, in 2017, in the film The Sound, in which the Lower Bay station was the main focus and setting of the story.