Barrie is one of the seven train lines of the GO Transit system in the Greater Toronto Area, Ontario, Canada. It extends from Union Station in Toronto in a generally northward direction to Barrie, and includes ten stations along its 101.4 kilometres (63.0 mi) route. From 1982 to 1990 and again from 1993 to 2007, it was known as the Bradford line, named after its former terminus at Bradford GO Station until the opening of Barrie South GO Station.

GO Transit rail services are provided throughout the Greater Toronto and Hamilton Area (GTHA) and the Greater Golden Horseshoe. The GO Transit rail fleet consists of 90 MPI MP40 locomotives and 979 Bombardier BiLevel Coaches. In 2023, the system had a ridership of 40,807,100 passengers per year. GO Transit started on May 23, 1967, running single-deck trains powered by diesel locomotives in push-pull configuration on a single rail line along Lake Ontario's shoreline. When GO trains began operation, they ran on tracks mostly owned the two major freight railways of Canada: Canadian National (CN) and CPKC. Over time, GO Transit have acquired tracks, ensuring GO Transit has control over track maintenance and expansion. Metrolinx currently owns 80% of the GO's rail corridors.