The marble facade of the building contains ornate detailing, and the Fifth Avenue entrance is flanked by a pair of stone lions that serve as the library's icon.

[34][35] Whether John Mervin Carrère or Thomas S. Hastings contributed more to the design is in dispute, but both architects are honored with busts located at the bottoms of each of Astor Hall's two staircases.

[42] Starting in 1910, around 75 miles (121 km) worth of shelves were installed to hold the collections that were designated for being housed there, with substantial room left for future acquisitions.

[51] The first item called for was Philosophy of the Plays of Shakespeare Unfolded by Delia Bacon, although this was a publicity stunt, and the book was not in the Main Branch's collection at the time.

[47][62] The first item actually delivered was N. I. Grot's Nravstvennye idealy nashego vremeni ("Ethical Ideas of Our Time"), a study of Friedrich Nietzsche and Leo Tolstoy.

[47][63] The Beaux-Arts Main Branch was the largest marble structure up to that time in the United States,[51] with shelf space for 3.5 million volumes spread across 375,000 square feet (34,800 m2).

[45] In 1971, New York Times architectural critic Ada Louise Huxtable wrote, "As urban planning, the library still suits the city remarkably well" and praised its "gentle monumentality and knowing humanism".

[68] Architectural historian Kate Lemos wrote in 2006 that the library "has held a commanding presence at the bustling corner of 42nd Street and Fifth Avenue as the neighborhood grew up around it".

[69] Other patrons included First Lady of the United States Jacqueline Kennedy Onassis; writers Alfred Kazin, Norman Mailer, Frank McCourt, John Updike, Cecil Beaton, Isaac Bashevis Singer, and E. L. Doctorow; actors Helen Hayes, Marlene Dietrich, Lillian Gish, Diana Rigg, and Princess Grace Kelly of Monaco; playwright Somerset Maugham; film producer Francis Ford Coppola; journalists Eliezer Ben-Yehuda and Tom Wolfe; and boxer Joe Frazier.

[47][69] During World War II, American soldiers decoded a Japanese cipher based on a Mexican phone book whose last remaining copy among Allied nations existed at the Main Branch.

[72] Thomas Hastings prepared plans for new wings near the north and south sides of the structure, which would extend eastward toward Fifth Avenue, as well as a storage annex in Bryant Park to the west.

[80] In 1937, the doctors Albert and Henry Berg made an offer to the library's trustees to donate their collections of rare English and American literature.

Their tasks included upgrading the heating, ventilation, and lighting systems; refitting the treads on the branch's marble staircases; painting the bookshelves, walls, ceilings, and masonry; and general upkeep.

[86] Paul North Rice, who served as Chief of the Reference Department and directed the main branch from 1937 to 1953,[87] significantly expanded the collection during his tenure.

[103][114] Before the master plan was implemented, the D. S. and R. H. Gottesman Foundation gave $1.25 million in December 1981 for the restoration of the main exhibition room,[89] which was redesigned by Davis Brody and Cavaglieri.

[119][102] In the late 1980s, the New York Public Library decided to expand the Main Branch's stacks to the west, underneath Bryant Park.

[128] The library added more than 120,000 square feet (11,000 m2) of storage space and 84 miles (135 km) of bookshelves under Bryant Park, doubling the length of the stacks in the Main Branch.

In December 2005, the Lionel Pincus and Princess Firyal Map Division space, with richly carved wood, marble, and metalwork, was restored.

[149] Nicolai Ouroussoff, former architecture critic for The New York Times, opined that Foster's selection was "one of a string of shrewd decisions by the library that should put our minds at ease".

[161] The NYPL commissioned EverGreene Architectural Arts to recreate the mural in the Bill Blass Public Catalog Room, which had been severely damaged during its 105-year history.

[182][183] In November 2023, while the library was closed for Thanksgiving, protestors demonstrating for Palestine caused $75,000 in damage to the facade, amid a budget crisis for the NYPL.

[65] Two lion sculptures, made of Tennessee marble and sculpted by the Piccirilli Brothers based on a design by Edward Clark Potter, flank the stairway from 41st Street.

[205] Their original names, "Leo Astor" and "Leo Lenox" (in honor of the library's founders) were transformed into Lord Astor and Lady Lenox (although both lions are male), and in the 1930s they were nicknamed "Patience" and "Fortitude" by Mayor Fiorello La Guardia, who chose the names because he felt that the citizens of New York would need to possess these qualities to see themselves through the Great Depression.

These columns support a marble attic with six 11-foot-high (3.4 m) allegorical sculptures designed by Paul Wayland Bartlett; the figures flank three carved plaques, one each for the Astor, Lenox, and Tilden foundations.

[222] The west side, which faces Bryant Park, contains narrow vertical windows that illuminate the stacks inside the Main Branch.

[234] The north–south corridor extends the entire width of the first floor, with large windows overlooking the street at either end; the ceiling was painted to resemble carved wood.

[245] The rotunda's walls contain red marble bases with dark wood piers, topped by a Corinthian entablature with dentils and modillions.

The work includes four large panels, two lunettes above doorways to the Public Catalog and Salomon Rooms, and a ceiling mural painted on the barrel vault.

[241][63][142][135] Characterized by Robert A. M. Stern as one of the United States' largest column-free rooms,[142] it is nearly as large as the Main Concourse at Grand Central Terminal.

It contains a conveyor belt and 24 small red carts emblazoned with the library's lion logo, which each carry up to 30 pounds (14 kg) of books between the stacks and the reading rooms.