These two volumes provide a critical edition of the Arabic text of the Great Introduction to Astrology (Kitāb al-mudḫal al-kabīr ilā ʿilm aḥkām an-nuǧūm) of Abū Maʿšar with a facing English translation. Keiji Yamamoto was primarily responsible for the Arabic text, and Charles Burnett for the English translation. A comprehensive listing of all the variations from the Arab text (either in content or in interpretation) in John of Seville and Hermann of Carinthia’s twelfth-century Latin translations, is given in the footnotes to the English translation, and texts which occur only in one or other of these translations are provided in appendixes. This enables the reader to follow the interpretation of the Great Introduction from the time of the author, in mid ninth-century Baghdad, into Spain, and the transfer of the work into Latin, so that its impact both in Islam under Abbasid rule, and in the Latin West, can easily be traced. Moreover, for the first time, the large fragment of a Greek translation, included in the Mysteria, is included, in an edition by the late David Pingree. Comprehensive glossaries of the vocabulary of the Great Introduction to Astrology and indexes of geographical places, peoples and constellations, all in Arabic, English, Greek and Latin (John of Seville) complete the volumes. The Latin texts can be consulted on the website of the Arabic and Latin corpus maintained by Dag Nikolaus Hasse at the University of Würzburg (http://arabic-latin-corpus.philosophie.uni-wuerzburg.de/)