Nasir al-Din Tusi, the renowned Shi'i scholar of the 13th century, produced a wide range of writings in different fields of learning under Ismaili patronage and later under the Mongols. "Contemplation and Action" is his autobiography, in which he recounts details of his early education, his search for knowledge and his eventual conversion to Ismaili faith. It is also a clear and vivid elaboration of the Ismaili doctrine of "ta'lim", the need for an authoritative teacher in spiritual knowledge. Translated for the first time into English, it is published here with the full Persian text and a substantial introductory essay on Tusi's life and thinking.