CTrain (previously branded C-Train) is a light rail system in Calgary, Alberta, Canada. The system is operated by Calgary Transit as part of the Calgary municipal government's transportation department, and currently consists of two lines; the Red Line and the Blue Line.

The CTrain began operation on May 25, 1981, and has expanded as the city has increased in population. In 2024, the system had a ridership of 94,097,200, or about 279,200 per weekday as of the second quarter of 2025, making it one of the busiest light rail transit systems in North America. Approximately 45% of workers in Downtown Calgary take the CTrain to work.

The idea for rail transit in Calgary originated in a 1967 Calgary transportation study, which recommended a two-line metro system to enter service in 1978. The original plans had called for two lines:

A third line, a north central line running from downtown to Thorncliffe mostly along Centre Street was also envisioned but was thought to be beyond the scope of the study.

However, a building boom in the 1970s had caused the heavy rail concept to fall out of favour due to the increased costs of construction, with light rail as its replacement. Light rail rapid transit (LRRT) was chosen over dedicated busways and the expansion of the Blue Arrow bus service (a service similar to bus rapid transit today) because light rail has lower long-term operating costs and addressed traffic congestion problems. The Blue Arrow service ended in 2000.

The present-day CTrain originated in a 1975 plan, calling for the construction of a single line, from the downtown core (8 Street station) to Anderson Road (the present-day Anderson station). The plan was approved by City Council in May 1977, with the construction of what would become the C-Train's "South Line" beginning one month later. The South Line opened on May 25, 1981. Oliver Bowen, a descendant of original black settlers to Amber Valley, Alberta Obadiah Bowen and Willis Reese Bowen, was the manager of the department that designed and built the original CTrain system. In 2009, the City of Calgary named its largest maintenance facility after Bowen to honour his work. The Oliver Bowen LRT Maintenance Facility (OBMF) in northeast Calgary is a $6.5 million rail facility.

Though the South Line was planned to extend to the northwest, political pressures led to the commission of the "Northeast Line", running from Whitehorn station (at 36 Street NE and 39 Avenue NE) to the downtown core, with a new downtown terminal station for both lines at 10 Street SW, which opened on April 27, 1985.

The Northwest Line, the extension of the South Line to the city's northwest, was opened on September 17, 1987, in time for the 1988 Winter Olympics. This line ran from the downtown core to University station, next to the University of Calgary campus. Since then, all three lines have been extended incrementally, with most of the stations commissioned and built in the 2000s (with the exception of Brentwood which opened in 1990, three years after the original Northwest line opened).