Aristotle’s four elements—earth, air, fire, and water—are the simplest bodies in the sublunary region. A closer look at Aristotle’s discussions of the four elements raises a number of questions: for example, it is unclear whether they are compounds of matter and form, or whether they can survive changes in their qualitative features. This book offers a study of Aristotle’s sublunary elements, with a focus on their relationships to changes in the categories of substance, quality, quantity, and place. In doing so, the book brings together Aristotle’s discussions of sublunary elements from On Generation and Corruption, De Caelo, and the Physics. It contributes to a new interpretation of Aristotle’s sublunary elements as substances that have their own powers.