collection of books and manuscripts gathered during the 15th century in Florence by Cosimo the Elder (Medici, Cosimo de') and Lorenzo the Magnificent (Medici, Lorenzo de'), both members of the Medici family. Part of the collection was open to the public before 1494, but in that year the Medici were overthrown and their palace was sacked. What remained of the library was taken to Rome, where it was kept by Lorenzo's son Giovanni, who was elected pope (Leo X) in 1513. When Lorenzo's nephew Giulio was elected pope ( Clement VII) in 1523, he returned the library to Florence and commissioned Michelangelo to construct a suitable building. The first drawings for the building were made in 1523. The carved ceiling was designed in the same year but finished 10 years later by two indifferent craftsmen. The mosaic floor, which repeats the design of the ceiling, and the carved benches were made by various assistants from sketches of the master. Michelangelo's designs for the staircase of the library were finished by Bartolomeo Ammanati and Giorgio Vasari in 1559.

Though it was unfinished, the library was opened in 1571. Its principal importance lies in its 10,500 manuscripts, more than 700 of which date from before the 11th century. Some are among the most valuable codices in the world—a famous Virgil of the 4th or 5th century, the Justinian Pandects of the 6th, a Horace of the 10th, many other very early classical and biblical texts, approximately 100 codices of Dante, a Decameron copied by a contemporary from Giovanni Boccaccio's own manuscript, and Benvenuto Cellini's manuscript of his autobiography.