The Kitchener line is one of the seven passenger rail lines of the GO Transit system in the Greater Toronto Area, Ontario, Canada. It extends westward from Union Station in Toronto to Kitchener, though most trains originate and terminate in Brampton in off-peak hours.

The GO Transit Georgetown line opened on April 29, 1974, becoming the second line in the GO Transit rail network. Peak-direction train service operated between Georgetown and Union Station, replacing a commuter service previously operated by Canadian National Railway (CN).

Service was extended beyond Georgetown to Guelph on October 29, 1990, but was again cut back to Georgetown on July 2, 1993.

Limited weekday midday service was introduced in April 2002, with four trains in each direction between Union and Bramalea. These trains were discontinued in 2011 to facilitate construction of the Georgetown South Expansion project.

On December 19, 2011, the Georgetown Line was renamed the Kitchener Line as service was extended to Kitchener, making one intermediate stop at Guelph. Another intermediate stop, Acton, opened on January 7, 2013.

Weekday midday service was re-introduced in September 2015, with hourly service between Mount Pleasant and Union.

In September 2019, GO Transit introduced limited off-peak train service along the entire length of the line, with two new weekday round trips operating between Toronto and Kitchener outside of peak periods.

On October 18, 2021, service to London, Ontario began as a pilot project; one train per weekday in each direction runs as an extension of Kitchener line service, with intermediate stops in Stratford and St. Marys. The existing Via Rail station in each community served as each stop. Service beyond Kitchener was discontinued following the end of the project, on October 13, 2023. On July 6, 2026, service will return to Stratford with the addition of a weekend train running from Toronto to Stratford in the morning and back in the evening.