Book excerpt: Ever since a group of people came into existence who called themselves Muslims and followed Islam, questions of what it means to be a member of this group - who is to be included/excluded and what the requirements for membership are - have proven to be both divisive and defining. For scholars and critics, the issue of what constitutes or defines 'Islam' - whether examining the history of the religion, its specific traditions, sectarian politics, or acts of terrorist - is central to any understanding of issues, cultures and ideas. 'Defining Islam' brings together key classic and contemporary writings on the nature of Islam to provide student readers with the ideal collection of both primary and critical sources.