The essays in this volume reflect the wide-ranging interests of John D. North, distinguished historian of science and philosophy. Section one has papers on horoscopes, astrolabes and time-reckoning, and it includes an edition of a 12th century treatise on the astrolabe and surveys of astrolabes. Section two is devoted to the study of the medieval cosmos. These contributions discuss Calcidian astronomy, astronomy in Spain’s Jewish community, the role of God in scholastic natural philosophy, and other themes. New information is presented about previously unknown scholars such as Abd al-Masih of Winchester and Simon Bredon. Section three contains essays on philosophy and scholarship in the early modern period, including pieces about commentaries on Boethius’s Consolatio Philosophiae in the Northern renaissance, Spinozistic philosophy, and the early modern concept of substance. These essays take up the various themes to which John D. North has made important contributions: the development of scientific knowledge and methodology, the style of scientific and philosophical thought, and the uses of scientific knowledge in the making of instruments or the casting of horoscopes.