The Delhi Metro is a rapid transit system that serves Delhi and the adjoining satellite cities of Faridabad, Gurugram, Noida, Bahadurgarh, and Ballabhgarh in the National Capital Region of India. The system consists of 10 colour-coded lines serving 289 stations, with a total length of 395 km (245 mi). It is India's largest and busiest metro rail system and the second-oldest, after the Kolkata Metro. The metro has a mix of underground, at-grade, and elevated stations using broad-gauge and standard-gauge tracks. The metro makes over 4,300 trips daily.
Construction began in 1998, and the first elevated section (Shahdara to Tis Hazari) on the Red Line opened on 25 December 2002. The first underground section (Vishwa Vidyalaya – Kashmere Gate) on the Yellow Line opened on 20 December 2004. The network was developed in phases. Phase I was completed by 2006, followed by Phase II in 2011. Phase III was mostly complete in 2021, except for a small extension of the Airport Line which opened in 2023. Construction of Phase IV began on 30 December 2019.
The Delhi Metro Rail Corporation (DMRC), a joint venture between the Government of India and Delhi, built and operates the Delhi Metro. The DMRC was certified by the United Nations in 2011 as the first metro rail and rail-based system in the world to receive carbon credits for reducing greenhouse-gas emissions, reducing annual carbon emission levels in the city by 630,000 tonnes.
The Delhi Metro has interchanges with the Rapid Metro Gurgaon (with a shared ticketing system) and Noida Metro. On 22 October 2019, DMRC took over operations of the financially-troubled Rapid Metro Gurgaon. The Delhi Metro's annual ridership was 203.23 crore (2.03 billion) in 2023. The system will have interchanges with the Delhi-Meerut RRTS, India's fastest urban regional transit system.