The New York Public Library (NYPL) is one of the leading public libraries of the world and is one of America's most significant research libraries. It is unusual in that it is composed of a very large circulating public library system combined with a very large non-lending research library system. It is simultaneously one of the largest public library systems in the United States and one of the largest research library systems in the world. It is a privately managed, nonprofit corporation with a public mission, operating with both private and public financing. Its flagship building, on Fifth Ave. running from 40th to 42nd Street in Manhattan, is a National Historic Landmark.

The historian David McCullough has described the New York Public Library as one of the five most important libraries in America, the others being the Library of Congress, the Boston Public Library, and the university libraries of Harvard and Yale.

Although it is called the "New York Public Library" the system does not cover all five boroughs of America's largest city, only Manhattan, The Bronx and Staten Island. New York City does not have a single public library system but three of them. The other two are the Brooklyn Public Library and the Queens Borough Public Library, serving the boroughs of Brooklyn and Queens, respectively. This came about because these three library systems predate the consolidation of New York City in 1898.

Currently, the New York Public Library consists of 87 libraries: four non-lending research libraries, four main lending libraries, a library for the blind and physically handicapped, and 77 neighborhood branch libraries in the three boroughs served. All libraries in the NYPL system may be used free of charge by all visitors. As of 2006, the research collections contain 43,773,335 items (books, videotapes, maps, etc.) of which 15,803,585 are books. The Branch Libraries contain 7,055,138 items of which 4,345,393 are books. Together the collections total more than 50 million items, and the books number more than 20 million, a number surpassed by only the Library of Congress and the British Library. If the three public library systems of New York City were considered as a single entity this unified library would have 208 branches and a collection of more than 30 million book volumes, making it the largest public library in the world.