The authors have based their findings upon original sociological research into the different responses of British and French authorities to the increasing numbers of Muslims in prison. Interviews with inmates and prison staff in various prisons show that Britain and France make sharply different provisions for the practice of Islam. The well-established practice of Christian chaplaincy in British prisons has been so well adapted to the needs of Muslims that Islam is becoming institutionalised and cemented into the structure of prisons. By contrast, French prisons provide relatively few opportunities for Muslim prisoners to practise their religion under the leadership of qualified imams. Consequently, varieties of do-it-yourself Islam and of Muslim extremism flourish unofficially on the margins of French prisons. The book's conclusions point to the different policy implications of the British and French ways of responding to Muslim prisoners.