CMRL stands for Chennai Metro Rail Limited, a joint venture between the Government of India and the Government of Tamil Nadu that builds and operates the Chennai Metro

Planning for the Metro started in 2007-08 with construction commencing in February 2009. After testing in 2014, the first segment of the metro between the Alandur and Koyambedu stations on the Green Line began operations on 29 June 2015. On 21 September 2016, operations on the Blue Line commenced between Chennai Airport and Little Mount. The underground stretch from AG-DMS to Washermanpet of Blue Line opened on 10 February 2019, completing phase 1 of the Metro.

Three more lines covering a length of 118.9 km (73.9 mi) are under construction as part of the second phase. The Chennai Mass Rapid Transit System, operated by Indian Railways, is planned to be incorporated into the Chennai Metro. A light rail has been proposed to connect Tambaram of the Chennai suburban rail network with Velachery on the MRTS. Further extensions are also planned for the three lines under construction.

A single electrified line from Chennai Beach to Tambaram began operations in 1931 as part of the Chennai Suburban Railway. Two other rail lines were subsequently built connecting Chennai Central to Gummidipoondi and Tiruvallur in 1979.[3][4] In 1965, the Planning Commission evaluated the capacity of the transportation network in major metropolitan cities including Madras, and developed plans for further expansion of transportation amenities.[5][6] As a result, an initial stretch of the Chennai Mass Rapid Transit System (MRTS) between Chennai Beach and Chepauk opened in 1995 – the first elevated rail line in India. The MRTS later extended to Thirumayilai in 1997, to Thiruvanmiyur in 2004, and to Velachery in 2007.[7][8][9] In 2006, a modern metro rail system for Chennai was planned and would be modeled after the Delhi Metro.[10][11]

The Chennai Metro is a rapid transit system