Professor Gregg specializes in the history of Christianity to the year 700 and concentrates research and teaching in early Jewish, Christian and Muslim interpretations of a number of biblical and qur'anic "sacred stories" which the Hebrew Bible, Christian Bible and the Qur'an have in common. Social and political interactions between Jews, "pagans," Christians and Muslims in the late antique and early Byzantine periods are central interests in his historical work, as are developments internal to the Christian movement in its opening centuries: appropriations of Greek and Roman philosophy, disputes over orthodox and heterodox teachings, formation of the canon of Christian scriptures, emergence of ritual practices, creeds, and church institutions. He received his PhD from the University of Pennsylvania.