Yonge Street (; pronounced "young") is a major arterial route in the Canadian province of Ontario connecting the shores of Lake Ontario in Toronto to Lake Simcoe, a gateway to the Upper Great Lakes. Until 1999, the Guinness Book of World Records repeated the popular misconception it was 1,896 km (1,178 mi) long, making it the longest street in the world; this was due to a conflation of Yonge Street with the rest of Ontario's Highway 11. Yonge Street (including the Bradford-to-Barrie extension) is only 86 kilometres (53 mi) long.The construction of Yonge Street is designated as an Event of National Historic Significance in Canada. Yonge Street was integral to the original planning and settlement of western Upper Canada in the 1790s, forming the basis of the concession roads in Ontario today. Once the southernmost leg of Highway 11, linking the provincial capital with northern Ontario, Yonge Street has been referred to as "Main Street Ontario". Today, no section of Yonge Street is marked as a provincial highway.

Ontario's first colonial administrator, John Graves Simcoe, named the street for his friend Sir George Yonge, an expert on ancient Roman roads. Yonge Street is a commercial main thoroughfare rather than a ceremonial one, with landmarks such as the Eaton Centre, Yonge-Dundas Square, and the Hockey Hall of Fame along its length. The Downtown Yonge shopping and entertainment district is named after it.

In Toronto and York Region, Yonge Street is the north-south baseline from which street numbering is reckoned east and west. The eastern branch of the subway Line 1 Yonge–University serves nearly the entire length of the street in Toronto; it serves as the spine of the Toronto subway system, linking to suburban commuter systems such as the Viva Blue BRT.