Brooklyn Rapid Transit Company in the context of "Jackson Heights–Roosevelt Avenue (IND Queens Boulevard Line)"

The New York City Subway is a rapid transit system that serves four of the five boroughs of New York City, New York: the Bronx, Brooklyn, Manhattan, and Queens. Its operator is the New York City Transit Authority, which is itself controlled by the Metropolitan Transportation Authority of New York. In 2015, an average of 5.65 million passengers used the system daily, making it the busiest rapid transit system in the United States and the 11th busiest in the world.

The present New York City Subway system is composed of three formerly separate systems that merged in 1940: the Interborough Rapid Transit Company (IRT), the Brooklyn–Manhattan Transit Corporation (BMT), and the Independent Subway System (IND). The privately held IRT, founded in 1902, constructed and operated the first underground railway line in New York City. The opening of the first line on October 27, 1904, is commonly cited as the opening of the modern New York City Subway, although some elevated lines of the IRT and BMT that were initially incorporated into the New York City Subway system but then demolished predate this. The oldest sections of elevated lines still in operation were built in 1885. The BMT, founded in 1923 and also privately held, was formed from the bankruptcy of the Brooklyn Rapid Transit Company. The IND was created by the City of New York in 1921 to be a municipally owned competitor of the two private companies. Unification in June 1940 by the New York City Board of Transportation brought the three systems under one operator. The New York City Transit Authority, created in 1953 to be a public benefit corporation that acquired the rapid transit and surface line (buses and streetcars) infrastructure of the Board of Transportation, remains the operator of the New York City Subway today.

The Dual Contracts, also known as the Dual Subway System, were contracts for the construction and/or rehabilitation and operation of rapid transit lines in the City of New York. The contracts were signed on March 19, 1913, by the Interborough Rapid Transit Company and the Brooklyn Rapid Transit Company. As part of the Dual Contracts, the IRT and BRT would build or upgrade several subway lines in New York City, then operate them for 49 years.

Most of the lines of the present-day New York City Subway were built or reconstructed under these contracts. The contracts were "dual" in that they were signed between the City and two separate private companies. Both the IRT and BRT (later Brooklyn–Manhattan Transit Corporation, or BMT) worked together to make the construction of the Dual Contracts possible.

The IRT Lexington Avenue Line (also known as the IRT East Side Line and the IRT Lexington–Fourth Avenue Line) is one of the lines of the A Division of the New York City Subway, stretching from Lower Manhattan north to 125th Street in East Harlem. The line is served by the 4, ​5, ​6, and <6> trains.

The line was constructed in two main portions by the Interborough Rapid Transit Company (IRT), a private operator. The first portion, from City Hall north to 42nd Street, was opened between 1904 and 1908, and is part of the first subway line in the city. The original subway turned west across 42nd Street at the Grand Central station, then went north at Broadway, serving the present-day IRT Broadway–Seventh Avenue Line. The second portion of the line, north of 42nd Street, was constructed as part of the Dual Contracts, which were signed between the IRT; the Brooklyn Rapid Transit Company, via a subsidiary; and the City of New York.