The hajj, the fifth pillar of Islam, is a religious duty to be performed once in a lifetime by all Muslims who are able. The Prophet Muhammad set out the rituals of hajjwhen he led what became known as the Farewell Hajjin 10 AH (632 AD). This set the seal on Muhammad's career as the founder of a religion and the leader of a political entity based on that religion. The convergence of the Prophet with the politician infuses the hajjwith political, as well as religious, significance. For the caliphs who led the Islamic community after Muhammad's death, leadership of the hajjbecame a position of enormous political relevance as it presented them with an unrivaled opportunity to proclaim their pious credentials and reinforce their political legitimacy. This unique study analyzes information provided by contemporary sources about the leadership of the Hajj in Islam's formative period, between the seventh and tenth centuries, and assesses the pilgrimage from a political perspective. A unique study because it collects and analyzes information provided by contemporary sources about the leadership of the Hajjin Islam's formative period, between the seventh and tenth centuries, and uses it to assess the pilgrimage from a political perspective. Published in advance of a major British Museum exhibition, The Hajj: Journey to the Heart of Islam, opening in London in January 2012. M.E. McMillanearned a PhD in Islamic history at the University of St Andrews, and has worked for the UN Security Council as a translator. The author lives in Belfast, Northern Ireland.