Book excerpt: This volume is the first collection of scholarly articles in any modern language devoted to Aristotle s "De caelo." It grew out of series of workshops held at Princeton, Cambridge, and Paris in the late 1990 s. Since Aristotle s "De caelo" had a major influence on cosmological thinking until the time of Galileo and Kepler and helped to shape the way in which Western civilization imagined its natural environment and place at the center of the universe, familiarity with the main doctrines of the "De caelo" is a prerequisite for an understanding of much of the thought and culture of antiquity and the Middle Ages.