He was from the Gīlān (province in northern Iran, on the southern coast of the Caspian Sea). He later moved to Rayy where he met Bīrūnī. He then moved to Jurjān in Ṭabaristān, a province adjacent to Gīlān, where he worked as the astronomer at the court of Wushmgīr ibn Ziyār (r. 935–67), the local ruler of the Ziyārid dynasty. We know from Bīrūnī that Kūshyār learned of the Sine Theorem from the work of his contemporary Abū Maḥmūd al-Khujandī’s and referred to it as al-shakl al-mughnī (literally, “The theorem that makes the [Menelaus Theorem] expendable”). Kūshyār’s major work in astronomy, the Zīj-i jāmi` (Universal/Comprehensive astronomical handbook with tables) was influenced by Ptolemy’s Almagest and Battānī’s zīj. Nasawī, who was supposed to have been Kūshyār’s disciple, wrote a commentary on Book I. Book I was translated into Persian about one century after Kūshyār. The entire Zīj was translated into Hebrew. Kūshyār’s Zīj-i bāligh (The extensive astronomical handbook with tables), to which he refers in the introduction to his astrological treatise, is not extant. Only a short chapter entitled “On the use of planets' cycles according the Indian method” remains in a Bombay manuscript. Kūshyār’s Risāla fī al-asṭurlāb (Treatise on the astrolabe) is extant in several manuscripts. Al-mudkhal fī ṣinā`at aḥkām al-nujūm (Introduction to astrology), also named Mujmal al-uṣūl fī aḥkām al-nujūm (Compendium of principles in astrology), is Kūshyār’s famous treatise on astrology, composed around 990; it is extant in numerous manuscripts. He was known for his work on astronomical handbooks (zījes) in addition to his work in mathematics and astrology. All his works are written in Arabic. For a detailed list of his works and their manuscripts see Sezgin 1974, pp. 343–345; 1978, pp. 246–249; and 1979, pp. 182–183. Also see Rosenfeld-Ihsanoğlu 2003, pp. 118–119; the following are emendations: the entry for M3 (on the principles of the composition of sine tables) was not written by Kūshyār ibn Labbān, but al-Battānī. (see Bagheri 1992). For A1 (Jāmi` Zīj ), Alexandria MS 4285c includes Book IV besides Book III (Rosenfeld-Ihsanoğlu only lists the latter); Vehbi MS 893 contains only Book IV; Revanköşk 1708 is a MS of A8 (on Astrology) rather than A1; Leiden Or. 8 and Leiden CCO 1054 both refer to the same MS of A1, whereas Leiden Or. 1021/3 turns out to contain sections I.7, I.8 and I.11 of A8. There is no MS of A1 in Tehran. There is a copy of A1 in the Russian State Library (previously Lenin Library) in Moscow, namely MS 154/3, which contains Books III and IV.  Tashkent MS 3894/1 (listed under A5)is an old Persian translation of Kūshyār’s treatise on the astrolabe (A3), and Irshād-i asṭurlāb (Majlis MS 6, Cat. vol. 1, p. 3, listed under A4) is not by Kūshyār. The Turkish translation of A8 by Mīkhālījī is Süleymaniye library, Hamidiye collection, MS 835. [M. Bagheri]