This new translation of De Caelo ( On the Heavens ) fits seamlessly with other volumes in the New Hackett Aristotle series, enabling Anglophone readers to study Aristotle’s work in a way previously not possible. The Introduction describes the book that lies ahead, explaining what it is about, what it is trying to do, how it goes about doing it, and what sort of audience it presupposes. Sequentially numbered endnotes provide the information most needed at each juncture, while a detailed Index indicates the places where focused discussion of key notions occurs.