These two volumes provide the Arabic, Latin and English text on historical astrology of the Middle Ages. The text is attributed either to Abu Ma'sar (787-886) or to his pupil Ibn al-Bazyar, and was translated into Latin in the mid-12th century. In eight books (parts) it provides the scientific basis for predictions concerning kings, prophets, dynasties, religions, wars, epidemics and more, by means of conjunctions of planets and other astrological phenomena, comets and other astronomical factors. It is cited frequently by both Arabic and Latin authors. These editions provide the context of these citations. Aside from its interest for cultural history and the history of science, the work provides several details concerning Islamic history.