»What Is Islam?« Usually Islam is considered as a plurality of tenets that can hardly be summed up in a coherent system. In opposition to this thesis, Nagel argues that Islam emerges in late antiquity as an independent and clearly defined religious faith rejecting the core of Christianity. Allah is the omnipotent Lord who is continuously involved in mundane affairs leaving to humankind no place for self-determined activities. Nagel analyses the outlines of nascent Islam and then deals in great detail with the social and political consequences ensuing from the message of the prophet Muhammed. Finally he tackles the problems of a sober appraisal of Islam Europe has met with since the days of Enlightenment.