This is the first translation into English of Seh Asl (Three Principles) by the important sixteenth century thinker Mulla Sadra. It contains a detailed introduction by Colin Turner that contextualizes the work and a footnoted commentary on the text itself. Also included is an epilogue and glossary. This work is of particular contemporary relevance as it represents the first tract against Islamic fundamentalism and will be of great interest to those studying Shi'ism and the history of Iran. .