These two volumes provide the Arabic, Latin and English text of the major work on historical astrology of the Middle Ages. The text is attributed either to Abu Ma’sar (787-886) or to his pupil Ibn al-B zy r, and was translated into Latin in the mid-twelfth century. In eight books (parts) it provides the scientific basis for predictions concerning kings, prophets, dynasties, religions, wars, epidemics etc., by means of conjunctions of planets, comets and other astronomical factors. It is cited frequently by both Arabic and Latin authors. These editions will provide, for the first time, the context of these citations. Aside from its intrinsic interest for cultural history and the history of science, this work provides several details.