The New York City Subway is a large rapid transit system and has a large fleet of electric multiple unit rolling stock. As of November 2016^[update], the New York City Subway has 6418 cars on the roster.

The system maintains two separate fleets of passenger cars: one for the A Division (numbered) routes, the other for the B Division (lettered) routes. All A Division equipment is approximately 8 feet 9 inches (2.67 m) wide and 51 feet (15.54 m) long. B Division cars, on the other hand, are about 10 feet (3.05 m) wide and either 60 feet 6 inches (18.44 m) or 75 feet 6 inches (23.01 m) long. The A Division and B Division trains operate only in their own division; operating in the other division is not allowed. All rolling stock, in both the A and B Divisions, run on the same 4 foot 8.5 inches (1,435 mm) standard gauge and use the same third-rail geometry and voltage. A typical revenue train consists of 8 to 10 cars, although in practice they can range between 2 and 11 cars.

The subway's rolling stock have operated under various companies: the Interborough Rapid Transit (IRT), Brooklyn–Manhattan Transit (BMT), and Independent Subway System (IND), all of which have since merged into the New York City Transit Authority. Cars purchased by the City of New York since the inception of the IND and for the other divisions beginning in 1948 are identified by the letter "R" followed by a number. Various kinds of cars are also used for maintenance work, including flatcars and vacuum trains.

As of November 2016^[update], the New York City Subway has 6418 cars on the roster.^{[2][lower-alpha 1]} The system maintains two separate fleets of passenger cars: one for the A Division routes, the other for the B Division routes. All A Division equipment is approximately 8 feet 9 inches (2.67 m) wide and 51 feet (15.54 m) long. B Division cars, on the other hand, are about 10 feet (3.05 m) wide and either 60 feet 6 inches (18.44 m) or 75 feet 6 inches (23.01 m) long. The 75-foot cars, the R44s, R46s, R68s, and R68As, are not permitted on BMT Eastern Division – the J, L, M, and Z trains – because of sharper curves on those tracks.

All rolling stock, in both the A and B Divisions, run on the same 4 foot 8.5 inches (1,435 mm) standard gauge and use the same third-rail geometry and voltage. However, trains operate only in their own division; operating in the other division is not allowed. A Division sections have narrower tunnel segments, tighter curves, and tighter platform clearances than the B Division sections, so B Division trains cannot fit in the A Division tunnels and stations, while A Division trains would have an unacceptably large gap between the platform and train if they were allowed in service on B Division lines. Also, the safety train stop (trip cock) mechanism is not compatible between divisions, being located on opposite sides of the track and train in each division. However, service and maintenance trains are composed of A Division-sized cars, so they can operate with either division's clearances and have safety train stops installed on both sides of the trucks.

A typical revenue train consists of 8 or 10 cars. The exceptions are the Franklin Avenue Shuttle, which runs 2-car trains; the Rockaway Park Shuttle, which runs 4-car trains; the 42nd Street Shuttle, which runs 6-car trains; the G, which runs 5-car trains; and the 7, which runs 11-car trains.

When the Brooklyn Rapid Transit Company entered into agreements to operate some of the new subway lines, they decided to design a new type of car, 10 feet (3.05 m) wide and 67 feet (20.42 m) long. The subject of several patents, the car's larger profile was similar to that of steam railroad coaches, permitting greater passenger capacity, more comfortable seating, and other advantages. The BRT unveiled its design, designated BMT Standard, to the public in 1913 and received such wide acceptance that all future subway lines, whether built for the BRT, the IRT, or eventually the IND, were built to handle the wider cars.

When the R44s and R46s were rebuilt, the rollsigns on the side of the cars were replaced with electronic LCD signs while the front service sign remained as a rollsign. In sharp contrast, the rebuilt R32s and R38s retained rollsigns on the sides, but a flip-dot display was placed in the front. The MTA has been incorporating newer subway cars into its stock in the past two decades. Since 1999, the R142s, R142As, R143s, R160s, R179s, and R188s have been added into service.^[3][4] All cars built since 1992 (including the now out-of-service R110As and R110Bs) are equipped with digital signs on the front, sides, and interior (except for the R110Bs, which had rollsigns on the front).

Old cars, some from the original companies (IRT, BMT, and IND), are preserved at the New York Transit Museum, while others have been sold to private individuals and/or other railway/trolley museums. Private companies include Railway Preservation Corp., whose equipment is often used on New York Transit Museum-sponsored excursions.

Between 1984 and 1989, some of the IRT trains were painted red, giving them the name Redbirds.^{[lower-alpha 2]} By January 2022, various older B Division cars, such as the entire fleets of R32s, R38s, R40s, R40As, R42s, and NYCT R44s, were similarly retired and replaced by newer models, including the R160s and R179s.

Various kinds of cars are used for maintenance work, including flatcars and vacuum trains.^[44]

• Air conditioning is standard on all cars R42 and later. R38s 4140–4149 and R40s 4350–4549 were also delivered with A/C, and all cars not equipped with A/C from classes R26–R40 (with the exception of the R27, R30, and R33S) were later retrofitted with A/C. All active cars are equipped with air conditioning, and cars with malfunctioning air conditioning are not supposed to be put into service.^[57]
• During World War II, a group of late-19th-century New York elevated cars was sent west to the San Francisco Bay Area by the United States Maritime Commission for use by the Shipyard Railway, a temporary wartime electric line transporting workers to the Kaiser Shipyards. After the war, most were sold to be used as units in a local motel, but their whereabouts afterward is unknown. Two of them, however, were acquired and have been restored by the Western Railway Museum in Rio Vista, California.^[58]
• There are many examples of rolling stock built under contract that are not intended for revenue services, such as the R95 money train, R65 pump train, R127/R134 garbage train, and R156 work locomotive.^[59]
• After the September 11th attacks, an American flag decal was added to every active subway car in the system. This practice continued with new car orders through the early 2020s.^[60][61]
• The table below shows what year the TA had expected to retire several car models in 1981.^[62]