The Mumbai Suburban Railway (Marathi: मुंबई उपनगरीय रेल्वे) is a mass transit system serving the Mumbai Metropolitan Region. It is part of the public transport system of Mumbai, is provided for by the state-run Indian Railways' two zonal Western Railways and Central Railways. The system carries more than 7.24 million commuters on a daily basis. It has the highest passenger densities of any urban railway system in the world. The trains plying on its routes are commonly referred to as local trains or simply as locals by the general populace.
The Mumbai Suburban Railway, as well as Indian Railways, are an offshoot of the first railway to be built by the British in India in April 1853, and was also the oldest railway system in Asia. The first train ran between Victoria Terminus (now Chhatrapati Shivaji Terminus) and Thane, a distance of 34 km, on 16 April 1853 at 3:35PM. The Bombay Railway History Group has been striving to document railway heritage along this line.
Due to the geographical spread of the population and location of business areas, the rail network is the principal mode of mass transport in Mumbai. As Mumbai's population swelled from a heavy inflow of migrants in recent decades, frequent overcrowding has become a serious issue, and numerous safety concerns have been raised over the years. A metro system and a monorail system are under construction in Mumbai to ease the travelling conditions in the Suburban network.