Bernard E. Rollin, recipient of the prestigious PRIM&R's Lifetime Achievement Award in 2016, uses the concept of telos to claim that humans have a responsibility to treat animals ethically. Aristotle described the metaphysics of our world with his concept of telos, from the Greek word for “end” or “purpose,” as the core explanatory concept for the world we live in. We understand what an animal is by what it does—the “pigness” of the pig; the “dogness” of the dog. This is the nature of an animal, and helps us understand our obligations to animals in the same way the understanding of human nature helps determine our obligation to humans. This book, the culmination of forty years of theorizing about the moral status of animals, explicates and justifies society’s moral obligation to animals in terms of the commonsense metaphysics and ethics of telos.