The Laurentian Library (Biblioteca Medicea Laurenziana or BML) is a historic library in Florence, Italy, containing more than 11,000 manuscripts and 4,500 early printed books. Built in a cloister of the Medicean Basilica di San Lorenzo di Firenze under the patronage of the Medici pope Clement VII, the library was built to emphasize that the Medici were no longer just merchants but members of intelligent and ecclesiastical society. It contains the manuscripts and books belonging to the private library of the Medici family. The library building is renowned for its architecture that was designed by Michelangelo and is an example of Mannerism.

All of the book-bound manuscripts in the library are identified in its Codex Laurentianus. The library conserves the Nahuatl Florentine Codex, the Rabula Gospels, the Codex Amiatinus, the Squarcialupi Codex, and the fragmentary Erinna papyrus that contains part of her Distaff.

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. It was then continued by Tribolo, Vasari, and Ammannati based on plans and verbal instructions from Michelangelo. The library opened by 1571. In this way, the library integrates parts executed by Michelangelo with others built much later in an interpretation of his instructions. The Laurentian Library is one of Michelangelo's most important architectural achievements. Even Michelangelo's contemporaries realized that the innovations and use of space in the Laurentian Library were revolutionary.

The admirable distribution of the windows, the construction of the ceiling, and the fine entrance of the Vestibule can never be sufficiently extolled. 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. – Giorgio Vasari.

The two-story quattrocento cloister remained unchanged by the addition of the library. Because of this, certain features of Michelangelo's plan, such as length and width, were already determined. Therefore, new walls were built on pre-existing walls and cloisters. Because the walls were built on pre-existing walls, recessing the columns into the walls was a structural necessity. This led to a unique style and pattern that Michelangelo took advantage of.

The vestibule, also known as the ricetto, is 10.50 m long, 10.50 m wide, and 14.6 m tall (34.5 by 34.5 by 48 feet). It was built above existing monastic quarters on the east range of the cloister, with an entrance from the upper level of the cloisters. 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.

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) 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.

The plan of the stairs changed dramatically in the design phase. 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. A year later, the stairway was moved to the middle of the vestibule. Tribolo attempted to carry out this plan in 1550, but nothing was built. Ammannati took on the challenge of interpreting Michelangelo's ideas to the best of his abilities using a small clay model, scanty material, and Michelangelo's instructions.