Nasir al-din Tusi (13th century) has left us some of the most distinctive writings on the esoteric interpretation of words, whether written or spoken. The paramount role of ta’wil in the teachings of Ismaili Shi‘ism, from the earliest phase of its history until now, has been recognised both by experts on Ismaili studies and members of the Ismaili community alike. While Marshall Hodgson in his Order of the Assassins identifies the ta’wil as the “hallmark of the Fatimid Ismailism,” Henry Corbin has rightly pointed out that such a phenomenon cannot be considered as only “a Shi‘i tendency or a phenomenon which emerged relatively late” (Histoire de la philosophie, p. 20). Ta’wil emerged from the basic teachings of the Qur’an and attracted the attention of a substantial number of Muslim intellectuals, while Ismaili scholars who personally adhered to ta’wil expounded upon it in a more technical and specific manner. This paper will attempt to place Nasir al-Din Tusi in both historical and intellectual context by first reviewing the basic topic of ta’wil, then introducing the specific developments of ta’wil under the Fatimids and continuing into its further refinement under Nizari Ismailism. Tusi’s writings on ta’wil will be highlighted and analysed.