The devotional book with the coat of arms of Queen Isabella the Catholic, produced in the late 1490s was decorated by celebrated artists including the panel painters and Flemish Primitives Gerard David and Gerard Horenbout. This unique work of art with about 80 illuminations is now kept in The Cleveland Museum of Art, Cleveland (Ohio). The largest part of the decoration can be attributed to the anonymous artist The Master of the First Prayer Book of Maximilian and his workshop as well as to the Master of the Prayer Books of around 1500. This book of hours is here the subject of a detailed physical and art historical investigation, with a special focus on the context of its creation, contemporary artists, influences, the use of pattern and singular iconography. Apart from the facsimile edition of the entire manuscript, the investigation includes a study of more than one hundred related works of art.