This volume of fourteen essays explores the biology of Aristotle and the Early Peripatos (Theophrastus and the Physical Problems) in its various dimensions—how the study of the soul contributes to the foundation of the science of perishable life, what is the program of this science and its main explanatory strategies, whether it be the explanation of natural generation or the relationship of the animal to its surroundings. But the authors also explore what might be, to Aristotle, the unity of life, not only that of animals and plants, but also that of celestial bodies and the Prime Mover.