Although the Caliphate was formally abolished ninety years ago, it had already ceased to exist as a unitary and effectively administered political institution many centuries earlier. The ever widening gap between political ideal and historical reality is also reflected in the varying conceptualizations and theories of the Caliphate developed by Islamic religious scholars and Muslim intellectuals past and present. However, recent events in the Islamic world show that the idea of a Caliphate still appeals to Muslims of varying persuasions. This three-volume reference work tracks the history of the Caliphate as what many Muslims believe to be a genuine and authentic Islamic political institution: From its emergence in seventh-century Arabia until highly contested and controversial attempts of its revival at the beginning of the twenty-first century by radical Islamists in Afghanistan and Iraq. No matter how grandiose such interpretations of a seemingly archaic institution may be, they show the Caliphate's longevity as a rallying point - real or symbolic - for Muslims across the world. Volume I: Origins and Formation Volume II: Challenges and Fragmentation Volume III: Modern Interpretations