The relationship of the European Enlightenment to Islam has usually been analyzed by collating “attitudes” toward a religion conceived as constitutively non-European. Enlightenment thinkers made use of Islam and other major revealed religions to relativize and to mock the claims of the Christian church. However, the notion of Islam as irredeemably “other” to Europe is a modern projection. Many eighteenth-century people passed back and forth between Europe and lands dominated by Islam, changing their identity, language, or religion, seeking refuge or a reversal of fortunes. One such figure was Jean-Jacques Rousseau's father, Isaac. Rousseau was marked in multiple ways by the mobility between Europe and the Muslim world, and by the new ideas these crossings engendered. This study of Rousseau's treatment of Islam and the Islamic world in his life and work proposes another model for thinking about Europe and Islam in the Age of Enlightenment.