The ten volumes of graduals commissioned by Philippe Villiers de L'Isle, elected Grand Master of the Knights Hospitaller of St John in 1521, are one of the treasures of the Co-Cathedral of St John in Valletta. Their size and their extensive and very beautiful decoration cannot fail to impress the visitors who see them in their display cases, but behind their grandeur (in no small part due to their great size) lies a complex artistic and liturgical history, which is the subject of this detailed account by Dr Theresa Zammit Lupi. They were written in 1533, shortly before L'Isle Adam's death in 1534, and following a disastrous fire in the church of St Lawrence in Birgu. After the consecration of the new Co-Cathedral in Valletta, the graduals were moved to this church, where they have remained ever since, and, as Theresa Zammit Lupi ably shows in her historical account, remained in use there for more than four centuries, being repeatedly adapted for successive changes in the liturgy.