Proceedings of an international conference held at the College de France in 2001, the book is a set of 27 contributions in English and in French of well known experts both in Turkish and Middle Eastern history (11th-18th centuries) and in the history of Religions. The aim was to draw a large picture of the religious richness and complexity of the Seljuk and Ottoman worlds and to comment on the consequences in terms of heresies and syncretisms, two concepts which are currently revisited by the same token. The influence of the dualistic doctrinal legacy is particularly put in light. Simultaneously the effects of the religious context upon Ottoman society and politics are discussed extensively.