Michael Frassetto specializes in medieval European history, the history of Christianity, and Christian interfaith relations in the Middle Ages. A Fulbright Scholar, he did dissertation research in Berlin and received his Ph.D. from the University of Delaware. The former religion editor for the Encyclopaedia Britannica, he has published numerous articles in Britannica and other encyclopedias including the Oxford Dictionary of the Middle Age. He has written many articles on medieval religious and social history that have been published in scholarly journals and essay collections and is the editor of several essay collections including Christian Attitudes toward the Jews in the Middle Ages: A Casebook and The Origins of Heresy and Persecution in the Middle Ages: Essays on the Work of R. I. Moore. He is also the author of Christians and Muslims in the Middle Ages: From Muhammad to Dante, The Early Medieval World: From the Fall of Rome to the Time of Charlemagne, and The Great Medieval Heretics Five Centuries of Religious Dissent.​