This research project traces the background to the formation of Bangladesh as secular state (1971), through an analysis of the cultural-religious and political evolution which Bengal's population experienced in preceding centuries. Whereas Islam primarily spread in Bengal via the preaching activities of Sufi mystics hailing from outside the region, - the characteristics which Islamic mysticism obtained in Bengal were clearly sui generis, and were shaped via the extensive intermingling with pre-existing cultural-religious currents, including Vaishnavism and Yoga-Tantra. Mainly formed in the 15th, 16th and 17th century, this syncretic style of Islam has re-shaped and enriched a culture of religious tolerance, which has largely persisted through the period of British colonial rule and beyond. Yet dominant Western political debates have for too long presumed that the concept and practice of religious tolerance have primarily been the outcome of the European Enlightenment with its message of rationalism. This project's hypothesis poses that, though the idea of secularism, of the state's neutrality between religions, has come to Bengal in the twentieth century as part of a modernistic message - it could gain popularity largely due to the fact that the country already possessed tolerant religious traditions, including a tolerant form of Islam.