The Laurentian Library was commissioned in 1523 and construction began in 1525; however, when Michelangelo left Florence in 1534, only the walls of the reading room were complete.

Boldness and grace are equally conspicuous in the work as a whole, and in every part; in the cornices, corbels, the niches for statues, the commodious staircase, and its fanciful division, in all the building, as a word, which is so unlike the common fashion of treatment, that every one stands amazed at the sight thereof.

Originally, Michelangelo planned for a skylight, but Clement VII believed that it would cause the roof to leak, so clerestory windows were incorporated into the west wall.

Blank tapering windows—framed in pietra serena, surmounted by either triangular or segmental pediments, and separated by paired columns set into the wall—circumscribe the interior of the vestibule.

[2] Lit by windows in bays that are articulated by pilasters corresponding to the beams of the ceiling, with a tall constricted vestibule (executed to Michelangelo's design in 1559 by Bartolomeo Ammannati[1]) that is filled with a stair that flows up to (and down from) the entrance to the reading room, the library is often mentioned as a prototype of Mannerism in architecture.

Originally in the first design in 1524, two flights of stairs were placed against the side walls and formed a bridge in front of the reading room door.

[6][7] In the ricetto, critics have noted that the recessed columns in the vestibule make the walls resemble taut skin stretched between vertical supports.

The recessed columns superficially appear to be of the austere and undecorated Doric order, typically considered to have a more masculine character.

[citation needed] The dynamic sculpture of the staircase appears to pour forth like lava from the upper level and reduces the floor space of the vestibule in a highly unusual way.

[2] In sharp contrast to the vestibule and staircase, the reading room's evenly spaced windows set between pilasters in the side walls let in copious amounts of natural light and create a serene, quiet, and restful appearance.

[1] Notable additions to the collection were made by its most famous librarian, Angelo Maria Bandini, who was appointed in 1757 and oversaw its printed catalogues.

[10] The core collection consists of approximately 3,000 manuscripts, indexed by Giovanni Rondinelli and Baccio Valori in 1589, which were placed on parapets (plutei) at the library's opening in 1571.

The library conserves the Nahuatl Florentine Codex, the major source of pre-conquest information about Aztec life in the western hemisphere.