The Biblioteca Ambrosiana is a historic library in Milan, Italy, also housing the Pinacoteca Ambrosiana, the Ambrosian art gallery. Named after Ambrose, the patron saint of Milan, it was founded in 1609 by Cardinal Federico Borromeo, whose agents scoured Western Europe and even Greece and Syria for books and manuscripts. Some major acquisitions of complete libraries were the manuscripts of the Benedictine monastery of Bobbio (1606) and the library of the Paduan Vincenzo Pinelli, whose more than 800 manuscripts filled 70 cases when they were sent to Milan and included the famous Iliad, the Ilias Picta.

Federico Borromeo was an Italian cardinal and Archbishop of Milan, a prominent figure of Counter-Reformation in Italy. Federico was a hero of the plague of 1630, described in Alessandro Manzoni's historical novel, The Betrothed. He was a great patron of the arts and founded the Biblioteca Ambrosiana, one of the first free public libraries in Europe. In 1618 he added a picture gallery, donating his own considerable collection of paintings. His published works, mainly in Latin, number over 100. They show his interest in ecclesiastical archaeology, sacred painting, and collecting.