New York City Subway

The New York City Subway is a rapid transit system owned by the City of New York and leased to the New York City Transit Authority, a subsidiary agency of the state-run Metropolitan Transportation Authority. Opened in 1904, the New York City Subway is one of the world's oldest public transit systems, one of the world's most used metro systems, and the metro system with the most stations and the most trackage. It offers service 24 hours per day and every day of the year.

The New York City Subway is the largest rapid transit system in the world by number of stations, with stations in operation (, if stations connected by transfers are counted as single stations). Stations are located throughout the boroughs of Manhattan, Brooklyn, Queens, and the Bronx. The Staten Island Railway is not officially considered part of the subway, as it lacks a rail link with the subway system, so passengers to another borough take a ferry or bus. The Port Authority Trans-Hudson and the AirTrain JFK, in Manhattan and Queens respectively, accept the subway's MetroCard but are not part of the subway; thus, free transfers are not allowed.

The system is also one of the world's longest. Overall, the system contains 233 mi of routes, translating into 660 mi of revenue track; and a total of 846 mi including non-revenue trackage.

By annual ridership, the New York City Subway is the busiest rapid transit rail system in the United States and in the Western world, as well as the seventh busiest rapid transit rail system in the world; the metro (subway) systems in Beijing, Seoul, Shanghai, Moscow, Tokyo, and Guangzhou record a higher annual ridership. In 2015, the subway delivered over 1.76 billion rides, averaging approximately 5.7 million daily rides on weekdays and a combined 5.9 million rides each weekend (3.3 million on Saturdays; 2.7 million on Sundays). Ridership continues to increase, and on September 23, 2014, more than 6.1 million people rode the subway system, establishing the highest single-day ridership since ridership was regularly monitored in 1985.

All services pass through Manhattan except for the train, the Franklin Avenue Shuttle, and the Rockaway Park Shuttle. Large portions of the subway outside Manhattan are elevated, on embankments, or in open cuts, and a few stretches of track run at ground level. In total, 40% of track is not underground despite the "subway" moniker. Many lines and stations have both express and local services. These lines have three or four tracks. Normally, the outer two are used for local trains, while the inner one or two are used for express trains. Stations served by express trains are typically major transfer points or destinations.