The Ismailis consist of two main branches the' Nizari Ismailis and the Musta'lian Tayyibi Ismailis. Both have their roots in the Fatimid period of Ismaili history and differ primarily over their respective belief in the Imamat. that is, spiritual leadership of the community.
The Nizari branch believes in a living, physically present Imam. Their present and forty-ninth Imam is Prince Karim Aga Khan. The Musta'lian Ismailis believe that their twenty-first Imam, al-Tayyib, went into physical concealment (satr) and that while the Imamat continues in his line, authority in his physical absence is exercised by a vicegerent, da'i mutlaq, who acts on his behalf. In their encounter with modernity therefore, the two communities reflect a different pattern of historical and institutional development.
Professor Azim Nanji serves currently as Special Advisor to the Provost at the Aga Khan University. Most recently he served as Senior Associate Director of the Abbasi Program in Islamic Studies at Stanford University 2008-2010 and also lectured on Islam in the Department of Religious Studies. He was previously the of Director of the Institute of Ismaili Studies from 1998 - 2008.
Zulfikar Hirji is an Anthropologist and Social Historian of Muslim Societies and Cultures. He is currently Associate Professor of Anthropology at York University, Toronto. He was formerly a Research Associate at The Institute of Ismaili Studies, London, and Junior Research Fellow at Wolfson College, Oxford.