The M1 and M3 are two similar series of electric multiple unit rail cars made by the Budd Company for the Long Island Rail Road, the Metro North Railroad and Metro North's predecessors, Penn Central (Whose predecessor, the Pennsylvania Railroad, operated the LIRR) and Conrail. Originally branded by Budd as The Metropolitans, the cars are more popularly known under their model names, M1 (late 1960s/1970s cars) and M3 (1980s cars). The proper name for the Metro North series are the M1A and M3A respectively though they are colloquially called by the main LIRR designations for the sake of simplicity.
The Metropolitans, at the time of their introduction, were notable for their rounded ends and quarter-point sliding doors. The cars resembled long rapid transit cars more than commuter rail equipment and provided inspirations to the R44 and R46 series of cars for the sister New York City Subway. Both series were also the catalyst of change for their respective systems. The Metropolitans were high-performance cars capable of sustaining 100 mph (160 km/h) in service, though they would never run that fast. The LIRR upgraded its third rail from 650 vdc to 750 vdc to take advantage of the cars' performance. Both the LIRR and then-Central division introduced high-level platforms for all stations in electric territory and the LIRR.
The M1 cars are powered by a 148 horsepower (110 kW) GE 1255 A2 traction motor on every axle, while the M3 cars use GE 1251 motors with an output of 140 horsepower (100 kW).
A recently retired Metro-North M1A on the dead line at Harmon Shops, April 2006An M1 on the Long Island Rail Road at Jamaica.The M1 series were funded by both New York State and the then-fledgling Metropolitan Transportation Authority which gained operation of the lines partway though the order. Seven hundred and seventy M1s (9001-9770) were built for the LIRR between 1968 and 1973 and 178 M1As (8200-8377) were built for the then-Central division from 1971 and 1973.
On the heels of the success of the M1/M1As, the MTA and Budd then made a series of structurally similar cars for the New Haven Line. Built between 1972 and 1977, the M2s (initially branded by Budd as the Cosmopolitans) fully replaced the ex-New Haven EMU cars for use on the New Haven mainline and the New Canaan Branch. Budd and MTA would later licence the design to other manufacturers for updated versions.
In the early 1980s, the MTA began to expand electrification areas of both the LIRR and the then-newly rechristened Metro-North. With the M1 series design proven, the MTA put in an order for similar cars in 1982 with the first trains entering service in spring of 1984. Essentially compatible with the M1 series, the M3s had updated elements (largely mechanical, some cosmetic) and a far more subdued interior scheme. Traction motor cooling was added to the M3 at the cost of considerable weight. This created different acceleration and braking rates from the M1. While LIRR mixed M1s and M3s in the same consist, Metro-North chose not to. 174 M3s (9771-9944, with 9891 and 9892 renumbered to 9945 and 9946 after the Long Island Rail Road massacre) were produced for the LIRR between 1984 and 1986 with 142 M3As (8000-8141) produced for Metro North, arriving between 1984 and early 1985.
This order would be the second-to-last handled by Budd, which in April 1987 left the railroad business after taking the name "TransitAmerica" under which the last M3s were produced though their builders plates kept the Budd name. The M3's also have the distinction of being one of the last, if not the last, third rail-powered cars to have the "blinking lights" effect at third rail gaps.
With the arrival of the M3 series, the M1 and M1A cars each saw mid-life rebuilds in the late-1980s in order to prolong their useful life. In the mid-late 1990s, smaller overhauls also took place. Still, time began to take its toll on the original M1 cars and by the end of the 20th century the time for the cars was running short.
In 2000, the MTA awarded Bombardier Transportation the contract to build the replacement for the M1 series, the M7 series. With the arrival of the first M7s to the LIRR in 2002 and the first M7As to Metro North in 2004, the M1 series began to be slowly retired. The last LIRR M-1 cars were retired in January 2007 while a small number of M1A's remaining in service on Metro-North. In preparation of the retirement of the M1's, the Sunrise Trail chapter of the National Railway Historical Society hosted a "Farewell to the M1's" fan trip on November 4, 2006.
Metro-North plans to keep approximately 30 M1 cars in sporadic revenue service. This helps keep the cars ready for shuttle service to the new Yankee Stadium station in the Bronx on the Hudson Line. 
The M3 series is currently in the process of being given a midlife overhaul.  LIRR M3s 9893-94 have been given a minor interior makeover somewhat similar to the M7 cars as a test while a set of Metro-North M3A cars is being rehabilitated in a different updated scheme.
As of April 2007, Metro-North is spending $1 million for the development of a specification for an M-3 replacement car, the M-9. However, due to the rising costs of maintaining the M-7 fleet, the M-9 development project has been delayed. The LIRR has already procured funding for an initial 68 cars with more on the way.