The Mumbai Metro is a rapid transit (MRT) system serving the city of Mumbai and the wider Mumbai Metropolitan Region in Maharashtra, India. Mumbai Metropolitan Region Development Authority is the responsible authority for maintaining the metro system. Maha Metro is responsible for all the metro rail projects undergoing in Maharashtra except the Mumbai Metropolitan Area. The system is designed to reduce traffic congestion in the city, and supplement the overcrowded Mumbai Suburban Railway network. It is being built in three phases over a 15-year period, with overall completion expected in October 2026. Mumbai Metro is the sixth longest operational metro network in India with operational length of 46.4 km (28.8 mi) as of January 2023. When completed, the core system will comprise fourteen high-capacity metro railway lines and one metrolite line, spanning a total of 356.972 kilometres (221.812 mi) (24% underground, the rest elevated, with a minuscule portion built at- grade), and serviced by 286 stations.

Line 1 of the Mumbai Metro Line 1 is operated by Mumbai Metro One Private Limited (MMOPL), a joint venture between Reliance Infrastructure (69%), Mumbai Metropolitan Region Development Authority, (26%) and RATP Dev Transdev Asia, France (5%). While lines 2, 4, 6, 7 (under construction), 5 and their extensions (bidding in progress) will be built by the Mumbai Metropolitan Region Development Authority (MMRDA), the completely underground Line 3 (also under construction) will be built by Mumbai Metro Railway Corporation Limited (MMRCL). The total financial outlay for the expansion of the metro system beyond the currently operational Line 1 is ₹82,172 crore (equivalent to ₹980 billion or US$12.26 billion in 2020), to be funded through a mix of equity and bilateral, multilateral as well as syndicated debt. In another boost to connectivity, the Mumbai Metropolitan Region Development Authority (MMRDA) has decided to connect Mumbai and Virar with a Metro line.

In June 2006, Prime Minister Manmohan Singh laid the foundation stone for the first phase of the Mumbai Metro project, although construction work began in February 2008. A successful trial run was conducted in May 2013, and the system's first line entered into operation on 8 June 2014. Many metro projects were being delayed because of late environmental clearances, land acquisition troubles and protests.

The financial capital of India received its first Metro in June 2014, and nearly after 8 years, Mumbai welcomed its two new metro corridors 2A and 7, which are now partially operational. Chief Minister Uddhav Thackeray flagged off the new metro lines 2A and 7 on 2 April 2022. The line was opened for commercial operation on the same day of the inauguration in the evening from 8 PM onwards. The minimum fare is ₹10 for 3 km (1.9 mi), and the maximum fare is ₹50 for 30 km (19 mi). As a part of the Phase 1 plan, both metro corridors cover a 20 km (12 mi) route (Dahanukarwadi–Dahisar–Aarey). The Metro runs between Dahanukarwadi on Metro Line 2A and Aarey on Line 7.