This book presents an English-language translation of Risala-yi MuE iniya, or the MuE iniya Epistle. Risala-yi MuE iniya is one of the earliest known works of Nasir al-Din Tusi (1201-1274), an intellectual luminary of the 13th century CE. The work is notable for the choice of Tusi's native Persian as the language of the text. In addition, Tusi organized his volume into a four-part structure, which went on to become a popular template for the Islamic astronomers who succeeded him. This book helped ensure the patronage of Tusi's courtly patrons during his decades-long stay with the IsmaE ilis, as well as the continuation of his remarkable career under the first Ilkhanid rulers of Persia. This translation helps make this notable treatise accessible to English language readers. It is among a handful of English translations of major astronomical works dealing with hay'a/cosmography in the Islamic world. Subsequently Tusi was to pen his own commentary on the work (the Hall-i Mushkilat-i MuE iniya, or A solution to the difficulties of the MuE iniya) and he used this occasion to discuss his celebrated mathematical formulation "the Tusi Couple" (a concept that he merely hinted at in the Risala-yi MuE iniya).
