The cellar, which is not open to the public, is located below the ground floor.
It was initially used for a mechanical plant, and contains remnants of the original Croton Reservoir.

The ground floor contains the entrance to 42nd Street as well as the temporary branch of the Mid-Manhattan Library.
Originally it contained a coat-check, circulating library, newspaper room, and children's-book room.
There were also spaces for telephones, a "library-school office", and a "travelling-library office".
Room 80, originally the circulating library, is now part of Bartos Forum.
The former newspaper room in room 78 is now the children's-book room, and the former children's-book room in room 81 is now the temporary branch of the Mid-Manhattan Library.

Above the ground floor is the first floor.
The staircase entrance from Fifth Avenue opens up into the first-floor lobby, known as Astor Hall.
This floor contains the Picture Collection (room 100), Periodical Room (room 108), and Jewish Division (room 111, former Periodicals Room) on the south side.
On the north side are the Milstein Division (room 121, former Patents Room), Milstein Microforms (room 119), and Map Division (room 117).
The Wachenheim Gallery, the library shop, the Bartos Education Center, and the Gottesman Hall (room 111, former Exhibition Room) are located in rooms that open into Astor Hall.
The first floor also used to contain various supervisors' offices, a library for the blind, and a technology room.

The second floor contains the Jill Kupin Rose Gallery, which contains ongoing exhibitions.
This floor contains several small rooms extending to the north, west, and south.
One of these is the Wachenheim Trustees' Room, which contains wood paneling, parquet floors, and a fireplace made of white marble.
Originally, this level contained director's and assistant director's offices; the Slavonic, Jewish, and Oriental Collections; and rooms for science, economics and sociology, and public documents.
The former science room at room 225 is now the Cullman Center, while room 228, the former economics and sociology room, has been split into two rooms.

The third floor contains the McGraw Rotunda on the east side of the building.
A passageway called the Print Gallery extends to the building's southern side, and one publicly accessible room, the Wallach Division, is adjacent to the gallery.
Similarly, the Stokes Gallery extends northward, with the Berg and Pforzheimer Collections branching off of it.
The Salomon Room branches off the McGraw Rotunda to the east.
To the west is the Bill Blass Public Catalog Room, which leads into the large Rose Main Reading Room.

The western side of the building, from the cellar to the second floor, contains part of the Main Branch's storage stacks.
Supplementing the Main Reading Room, there are 21 other reading rooms in the Main Branch, including a ground-floor room with a cast-iron ceiling.
There were originally 1,760 seats in all of the reading rooms combined, of which 768 were located in the Main Reading Room.
The cellar, which is not open to the public, is located below the ground floor. It was initially used for a mechanical plant, and contains remnants of the original Croton Reservoir.
The ground floor contains the entrance to 42nd Street as well as the temporary branch of the Mid-Manhattan Library. Originally it contained a coat-check, circulating library, newspaper room, and children's-book room. There were also spaces for telephones, a "library-school office", and a "travelling-library office". Room 80, originally the circulating library, is now part of Bartos Forum. The former newspaper room in room 78 is now the children's-book room, and the former children's-book room in room 81 is now the temporary branch of the Mid-Manhattan Library.
Above the ground floor is the first floor. The staircase entrance from Fifth Avenue opens up into the first-floor lobby, known as Astor Hall. This floor contains the Picture Collection (room 100), Periodical Room (room 108), and Jewish Division (room 111, former Periodicals Room) on the south side. On the north side are the Milstein Division (room 121, former Patents Room), Milstein Microforms (room 119), and Map Division (room 117). The Wachenheim Gallery, the library shop, the Bartos Education Center, and the Gottesman Hall (room 111, former Exhibition Room) are located in rooms that open into Astor Hall. The first floor also used to contain various supervisors' offices, a library for the blind, and a technology room.
The second floor contains the Jill Kupin Rose Gallery, which contains ongoing exhibitions. This floor contains several small rooms extending to the north, west, and south. One of these is the Wachenheim Trustees' Room, which contains wood paneling, parquet floors, and a fireplace made of white marble. Originally, this level contained director's and assistant director's offices; the Slavonic, Jewish, and Oriental Collections; and rooms for science, economics and sociology, and public documents. The former science room at room 225 is now the Cullman Center, while room 228, the former economics and sociology room, has been split into two rooms.
The third floor contains the McGraw Rotunda on the east side of the building. A passageway called the Print Gallery extends to the building's southern side, and one publicly accessible room, the Wallach Division, is adjacent to the gallery. Similarly, the Stokes Gallery extends northward, with the Berg and Pforzheimer Collections branching off of it. The Salomon Room branches off the McGraw Rotunda to the east. To the west is the Bill Blass Public Catalog Room, which leads into the large Rose Main Reading Room.
The western side of the building, from the cellar to the second floor, contains part of the Main Branch's storage stacks. Supplementing the Main Reading Room, there are 21 other reading rooms in the Main Branch, including a ground-floor room with a cast-iron ceiling. There were originally 1,760 seats in all of the reading rooms combined, of which 768 were located in the Main Reading Room.
New York Public Library Main Branch