The Epistle of the Right Path (Risāla-yi Ṣirāṭ al-Mustaqīm) is an anonymous treatise, possibly dating to the late fourteenth or early fifteenth century. It may be the earliest Persian Ismaili prose work of the post-Mongol period to come to light, and is here introduced, discussed, edited and translated. A clearly articulated, philosophically inclined treatment of numerous themes in Ismaili thought, the text draws frequently from Nasir al-Din Tusi's spiritual autobiography, The Voyage (Sayr wa-Sulūk). Its subject matter includes the correspondence between the exoteric and esoteric worlds, the concept of the divine command through which creation attains perfection, the role of the Imam and the esoteric hierarchy, and the fact that esoteric exegesis (ta 'wīl) of divine revelation must be compatible with the principles of the intellect.