Josef van Ess, Emeritus Professor of Islamic Studies and Semitic Languages, University of Tubingen, Germany, has published widely on the History of the Islamic World; Islamic theology and philosophy, especially with respect to the formative period (8th-10th centuries) and the age of the Mongol conquests (13th-14th centuries); and Islamic mysticism. His most famous work and is Theologie und Gesellschaft in 6 volumes (de Gruyter 1991-97), the first four volumes of which are now being published in English by Brill. John O'Kane (1940) has been involved in various English translations of Arabic and Persian works to do with Sufism, and he has produced several English translation of works in the field of Islamic Studies originally published in German.