From the outset, the collecting of illuminated manuscripts at The Cloisters was considered a delicate procedure, to be followed with prudence. It was felt by those involved in acquisitions that the bulk of material there should be architectural elements, sculpture, and decorative arts—objects enhancing the environmental quality of the institution—and that manuscripts should more reasonably go to the incomparable Pierpont Morgan Library. It was a wise guideline, as the rare exceptions to it admirably attest. After more than thirty-five years of collecting, only four manuscripts are in the library of The Cloisters: the Belles Heures of Jean, Duke of Berry, the so-called Hours of Jeanne d'Evreux, the Hours of Bonne of Luxembourg, and the book that is the subject here. Each became part of The Cloisters Collection because each is one of those rarest works of art that seem to speak about the qualities and essences of fully an epoch of art history. The initial viewing of the Apocalypse manuscript while it was in possession of the dealer H. P. Kraus left no doubt but that this luminous fourteenth-century book, with its graceful paintings of near perfect balance, should join the very small group at The Cloisters. Subsequent discoveries about the book by Florens Deuchler have confirmed the immediate reaction. His discoveries, together with contributions by his colleague Jeffrey Hoffeld and by Helmut Nickel, Curator of Arms and Armor, are the substance of the present publication.