GO Transit is a regional public transit system serving the Greater Golden Horseshoe region of Ontario, Canada. With its hub at Union Station in Toronto, GO Transit's green-and-white trains and buses serve a population of more than seven million across an area over 11,000 square kilometres (4,200 sq mi) stretching from Kitchener in the west to Peterborough in the east, and from Barrie in the north to Niagara Falls in the south. In 2023, the system had a ridership of 56,036,900. GO Transit operates diesel-powered double-decker trains and coach buses, on routes that connect with all local and some long-distance inter-city transit services in its service area.

The Golden Horseshoe is a secondary region of Southern Ontario, Canada, which lies at the western end of Lake Ontario, with outer boundaries stretching south to Lake Erie and north to Lake Scugog, Lake Simcoe and Georgian Bay of Lake Huron. The region is the most densely populated and industrialized in Canada. Based on the 2021 census, with a population of 7,759,635 people in its core and 9,765,188 in its greater area, the Golden Horseshoe accounts for over 20 percent of the population of Canada and more than 54 percent of Ontario's population. It is part of the Quebec City–Windsor Corridor, itself part of the Great Lakes megalopolis.