Several of his books focus on Iran but deal also with the larger Muslim world, including The Patricians of Nishapur: a Study in Medieval Islamic History (1972), Conversion to Islam in the Medieval Period: An Essay in Quantitative History (1979), and Islam: the View from the Edge (1994).
Mehrere seiner Publikationen befassen sich mit dem Iran und mit der islamischen Welt im Ganzen: The Patricians of Nishapur: a Study in Medieval Islamic History (1972), Conversion to Islam in the Medieval Period: An Essay in Quantitative History (1979) und Islam: the View from the Edge (1994).