Following the completion of the construction of new St. Peter's in the second decade of the seventeenth century, a series of monumental altarpieces was commissioned to decorate its altars. The leading artists of the day contributed to the project - among them Algardi, Bernini, Cortona, Domenichino, Guercino, Lanfaranco, Poussin, Sacchi, Vouet, and Valentin - and the works they produced include some of the most celebrated masterpieces of the Roman Baroque. Here for the first time the altarpieces of St. Peter's are considered collectively, within the liturgical and artistic programme of the building as a whole. Louise Rice takes a comprehensive approach to this critical chapter in the history of Italian Baroque art, offering insight into the mechanisms, motives, and meanings of papal patronage in the premier church of Catholicism.