Nasir al-Din Tusi (d. 672/1274) was an influential philosopher, theologian, mathematician and astronomer, besides being the first director of the famous observatory at Maraghah near Tabriz as well as a man of politics. The author of a large number of works, he is especially famous for such treatises as his Tajrid al-i?tiqad on theology; the Zij-i Ilkhani on astronomy; the Hall mushkilat al-Isharat; his influential commentary on Avicenna's (428/1037) Kitab al-isharat wal-tanbihat on philosophy and logic; and his Akhlaq-i Nasiri on ethics. Another famous work is his Tadhkira fi ?ilm al-hay?a published here. As stated by the editor, this is one of the most important and influential astronomical works written in the pre-modern Islamic world. It belongs to the second phase of Tusi's academic career and constitutes a synthesis between two earlier works by him, written when he was still working for the Nizari Ismailis. Arabic text and apparatus, Persian introduction translated from the English edition.