The Sforza Hours, is a richly illuminated book of hours initiated by Bona Sforza, widow of Galeazzo Sforza, Duke of Milan, around 1490, who commissioned the illuminator Giovanni Pietro Birago. The book remained in an unfinished state for 30 years until Margaret of Austria, Regent of the Netherlands, commissioned its completion in 1517–20 from the artist Gerard Horenbout. The book therefore contains decoration of the highest quality by two artists. It provides a unique example of an early sixteenth-century Northern Renaissance illuminator's response to Milanese art of the late Quattrocento. The history of the Sforza Hours also includes one of the earliest recorded examples of art theft.

Bona of Savoy, Duchess of Milan was Duchess of Milan as the second spouse of Galeazzo Maria Sforza, Duke of Milan. She served as regent of Milan during the minority of her son 1476–1481.