form of prayer book developed in the 14th cent. from the prayers of clerics appended to the main service. The subjects of the miniature illustrations (see miniature painting) were frequently derived from the appendix of the Psalter. The book of hours served as a devotional work containing various prayers and meditations appropriate to seasons, months, days of the week, and hours of the day. Many such books are masterpieces of illumination and were symbols of refinement and wealth in fashionable houses of the 15th cent. Jean, duc de Berry, was among the most renowned collectors of books of hours, and his Très Riches Heures (Musée Condé, Chantilly), illustrated in part by the Limbourg brothers (c.1415), is among the greatest achievements in this genre.