John Jacob Astor placed a codicil in his will to leave $400,000 for a public library. When he died in 1848, the resulting board of trustees built the Astor Library in the East Village by 1854. It was a reference library only -- books could not leave the building. Meanwhile, bibliophile James Lenox donated his vast collection of Americana, manuscripts, and rare books to the Lenox Library, built on Fifth Avenue between 70th and 71st Streets in 1877. His collection included the first Gutenberg Bible in the New World. Former New York Governor Samuel J. Tilden died in 1886 and left the bulk of his fortune to establish a free public library. For years the money sat in a trust, until attorney John Bigelow and civic leader Andrew Haswell Green proposed merging the Astor and Lenox libraries with Tilden's endowment. On May 23, 1895, the three foundations were united as The New York Public Library, Astor, Lenox and Tilden Foundations. Andrew Carnegie later donated funds to build sixty-five branch libraries across the city, with the stipulation that New York City operate and maintain them.

The Main Branch occupies a central site along Fifth Avenue between 40th and 42nd Streets, built on top of what was once the Croton Reservoir. John Shaw Billings, the library's first director, conceived a massive reading room atop seven floors of book stacks with a system designed to get books into readers' hands as fast as possible. When it opened in 1911, it was the largest marble structure in the United States. The two stone lions guarding the entrance were sculpted by E.C. Potter and carved by the Piccirilli Brothers. The main reading room was the largest of its kind in the world. An expansion in the 1970s and 1980s added storage space beneath Bryant Park, directly west of the building. A major restoration from 2007 to 2011 was funded by a $100 million gift from Stephen A. Schwarzman, and the branch was renamed in his honor. Today the Rose Main Reading Room, Astor Hall, and the McGraw Rotunda are all designated New York City interior landmarks -- rooms where the architecture itself is legally protected.

The library's collections have played roles that extend far beyond quiet scholarship. During World War II, the military drew extensively from the library's map and book holdings, even hiring its staff. Walter Ristow, chief of the Map Division, became head of the geography section of the War Department's Military Intelligence office in New York from 1942 to 1945. He and his staff discovered, copied, and loaned thousands of strategic, rare, or unique maps to war agencies that could find the information nowhere else. In 1931, the library purchased the private library of Grand Duke Vladimir Alexandrovich, uncle of the last tsar, in one of the largest acquisitions of Russian books and photographic materials ever assembled. At the time, the Soviet government had a policy of selling its cultural treasures abroad for gold. Washington Irving, the author of "Rip Van Winkle" and "The Legend of Sleepy Hollow," served as president of the Astor Library's Board of Trustees from 1849 until his death in 1859, shaping its early collecting philosophy with his deep knowledge of European intellectual life.

In 2010, the NYPL moved back-office operations to a Library Services Center in Long Island City, housed in a renovated warehouse. In the basement sits a book-sorting machine that is two-thirds the length of a football field -- the largest of its kind in the world, according to library officials. Using bar codes, the machine sorts 7,500 items per hour with a team of fourteen employees, cutting inter-branch delivery times by at least a day. The third floor houses the Barbara Goldsmith Preservation Division, where damaged and aging materials are restored. The library has also digitized over 900,000 images from its collections, making them freely available online. Its digital holdings exceed a petabyte of data. In 2021, the NYPL eliminated late fees entirely, clearing all existing debts from patron records. The library also developed SimplyE, an open-source app that lets patrons browse and check out e-books from multiple vendors. Through its Books for All program, the NYPL makes banned books available to anyone in the United States via the app.

The New York Public Library is not a government agency. It is a private, non-governmental, independently managed nonprofit that has operated on both public and private funding since its founding. It serves Manhattan, the Bronx, and Staten Island through 89 neighborhood branches and four research centers. Brooklyn and Queens maintain their own separate library systems. The NYPL shares an off-site shelving facility in Plainsboro, New Jersey with the libraries of Harvard, Columbia, and Princeton through the Research Collections and Preservation Consortium. The Schomburg Center for Research in Black Culture sits at 135th Street and Lenox Avenue in Harlem. The Library for the Performing Arts occupies a home at Lincoln Center. Together, the research libraries hold approximately 44 million items. The branch collections add another 9.9 million. The library answers 100,000 reference questions per year through its ASK NYPL telephone service. And every day, New Yorkers of all kinds walk between Patience and Fortitude, past the marble columns, and into rooms where the accumulated knowledge of the world waits on open shelves.