The Encyclopedia of the Epistles of Purity is an esoteric Shia Islamic text written by the mysterious Brethren of Purity during the Buyid era. Composed of 52 treatises, it had a great influence on later intellectual leading lights of the Muslim world, such as Ibn Arabi, and was transmitted as far abroad within the Muslim world as al-Andalus.
The identity and period of the authors of the Encyclopedia have not been conclusively established, though the work has been mostly linked with Isma'ilism. Idris Imad al-Din, a prominent 15th-century Isma'ili missionary in Yemen, credited the authorship of the encyclopedia to Muhammad al-Taqi, the 9th Isma'ili Imam, who lived in occultation in the era of the Abbasid Caliphate at the beginning of the Islamic Golden Age.