The Caliphate by William Muir provides a comprehensive history of those 'successors of the apostle of God', the leaders of the Islamic community founded by the Prophet Muhammad at Medina.These were the Caliphs, rulers of the great Islamic Empire for over six centuries. Charged with the task of administering a vast empire, in their hands also resided the defence of the Islamic faith. This twofold responsibility produced leaders of outstanding courage, judgement and faith. Against a historical background, the author has highlighted the lives and characters of those extraordinary men who fought for the expansion and survival of a united Islamic Empire. In his original introduction the author offered his work as 'a contribution towards the history of the period for which there are, as yet, but scanty, materials in the English language'. The reprinting of this work will be no less welcome today as a continuing and valuable contribution to the field of Islamic study.