What is a person? Why do we count certain beings as persons and others not? How is the concept of a person distinct from the concept of a human being, or from the concept of the self? When and why did the concept of a person come into existence? What is the relationship between moral personhood and metaphysical personhood? How has their relationship changed over the last two millennia? This volume presents a genealogy of the concept of a person. It demonstrates how personhood--like the other central concepts of philosophy, law, and everyday life--has gained its significance not through definition but through the accretion of layers of meaning over centuries. We can only fully understand the concept by knowing its history. Essays show further how the concept of a person has five main strands: persons are particulars, roles, entities with special moral significance, rational beings, and selves. Thus, to count someone or something as a person is simultaneously to describe it--as a particular, a role, a rational being, and a self--and to prescribe certain norms concerning how it may act and how others may act towards it. A group of distinguished thinkers and philosophers here untangle these and other insights about personhood, asking us to reconsider our most fundamental assumptions of the self.