Protestants and Catholics of our day may continue to disagree regarding the Eucharist, but the debate is nothing new. In the ninth century AD, Radbertus and Ratramnus—two monks living in the same monastery—debated the nature of the Eucharist. A George J. Gatgounis argues in this text, understanding the debate between these “monastery mates” of the Middle Ages provides a solid foundation for discussing the basic issues of the current debate.