The C Line was a light rail line, part of the rail system operated by the Regional Transportation District in the Denver-Aurora Metropolitan Area in Colorado.

The line was added to the system on April 5, 2002, to coincide with the opening of the Central Platte Valley Spur. Initially, C trains operated seven days a week, but ran to Littleton–Mineral station only during peak hours and sporting events. At all other times, C service operated to I-25/Broadway.

On May 3, 2003, C trains began operating to Littleton–Mineral station at all times.

With the opening of the Southeast Corridor on November 17, 2006, weekend C service was discontinued except for certain sporting events, with the new E line operating seven days per week.

On January 11, 2009, the midday service pattern between Union Station and I-25/Broadway was resumed and evening service discontinued.

Midday weekday service was discontinued on January 19, 2012 and was reinstated on August 17, 2014 over the entire route.

The C Line was suspended on January 10, 2021 as part of broader service cuts in response to ridership decreases related to the COVID-19 pandemic. The line never returned to service and was officially eliminated ahead of the January 2023 service change.

The C Line's northern terminus was at Union Station in Denver, ran on a railroad right-of-way south to its junction with the D Line at 10th & Osage Station, and shared track with the D Line until both lines reach their southern terminus at Mineral Avenue in Littleton.

In addition, the C Line provided access to the sports venues of Denver – Coors Field, Pepsi Center, and Broncos Stadium at Mile High – Six Flags Elitch Gardens, and LoDo, as well as access to the western portion of the Auraria Campus.

Station	Municipality	Opening date	Interchange
Union Station	Denver	April 5, 2002	A  B  E  G  N  W  California Zephyr MallRide Flatiron Flyer
Ball Arena–Elitch Gardens			E  W
Empower Field at Mile High			E  W
Auraria West			E  W
10th & Osage		October 8, 1994	D  E  F  H
Alameda			D  E  F  H  Park and ride: 240 spaces
I-25 & Broadway			D  E  F  H  Park and ride: 1,248 spaces
Evans		July 14, 2000	D  Park and ride: 99 spaces
Englewood	Englewood		D  Park and ride: 910 spaces
Oxford–City of Sheridan	Sheridan		D
Littleton–Downtown	Littleton		D  Park and ride: 361 spaces
Littleton–Mineral			D  Park and ride: 1,227 spaces

The 2004 voter approved FasTracks plan will add 2.5 mi (4.02 km) to the Southwest Corridor (C Line and D Line). It will also add a station with 1,000 parking spots at C-470 and Lucent Boulevard in Highlands Ranch. There may also be a station at C-470 and Santa Fe Boulevard.

• RTD C Line Schedule