St. Clair Avenue is a major east-west street in Toronto, Ontario, Canada. It was laid out in the late 18th century by the British as a concession road (the Third Concession), 2 kilometres (1.2 mi) north of Bloor Street and 4 kilometres (2.5 mi) north of Queen Street.
St. Clair Avenue has two sections. The western section extends from Moore Park in the east to Scarlett Road in the west, a distance of approximately 10 kilometres (6.2 mi). An eastern section picks up on the far side of the Don Valley at Taylor Creek Park, extending for 7 kilometres (4.3 mi) to Kingston Road. Like all streets in Toronto which cross Yonge Street, St. Clair is divided into separate East and West sections, each with its own street numbers beginning at Yonge Street. Unlike most other concession-road streets in Toronto, St. Clair does not extend west into Etobicoke, due to the northern arc of Dundas Street crossing the Humber River near its western terminus, forming a link to Burnhamthorpe Road, its approximate equivalent arterial.
St. Clair Avenue West has heavy automotive and public transit traffic. Over half the commuters in rush hour traffic travel by the 512 St. Clair streetcar line which connects with St. Clair subway station on Line 1 Yonge–University and St. Clair West station also on the Line 1 Yonge-University subway.