Research interests: Jews in the Muslim world in the Middle Ages; documents from the Cairo Geniza.

Selected publications
Books
Under Crescent and Cross: The Jews in the Middle Ages, Princeton: Princeton University Press, 1994

The Autobiography of a Seventeenth-Century Venetian Rabbi:  Leon Modena's "Life of Judah",  Princeton: Princeton University Press, 1988

Al-Mujtama` al-Yahudi fi Misr al-islami fi al-`usur al-wusta,
translatyed into Arabic by Nasrir Marar and Samir Naqqash, The Jewish-Arab Institute and  Tel Aviv University, 1987

Jewish Self-Government in Medieval Egypt, Princeton University Press, 1980

Jews among Arabs:  Contacts and Boundaries, co-edited with A.L. Udovitch, Princeton: Darwin Press, 1989

Toward the Millennium:  Messianic Expectations from the Bible to Waco, co-edited with Peter Schaefer, Leiden: Brill, 1998