This study explores the phenomenon of Muslim apostasy from the perspective of self-described Muslim apostates. Drawing on life-history interviews with a group of ex-Muslims in Britain, it will provide a detailed qualitative account of what it means and what it is like for apostates to disaffiliate from Islam. It will also conduct interpretive narrative analysis of ex-Muslim published and online personal testimony, as well as semi-structured interviews with politically active Muslim 'career apostates'. The main focus of the study will be on the leaving-process and its ramifications as they are experienced and understood by apostates themselves. The key aims of the study are: to provide a close understanding of the experiences and narratives of Muslim apostates living in Britain to illuminate the dynamics by which individuals become Muslim apostates to describe the ramifications of apostatizing from Islam for the apostate and to document the various responses which the apostate's leave-taking provokes to map the political activities of Muslim 'career apostates', and to offer an account of their role. This study will be of interest not only to a broad range of sociologists, but also to policy-makers interested in the question of religious freedom, and social cohesion more broadly, in contemporary multicultural societies.