How does an entity become a person? Forty years ago Carl Rogers answered this question by suggesting that human beings become persons through a process of personal growth and self-discovery. In the present paper I provide six different answers to this question, which form a hierarchy of empirical projects and associated criteria that can be used to understand human personhood. They are: (1) persons are constructed out of natural but organic materials; (2) persons emerge as a form of adaptation through the process of evolution; (3) persons develop ontogenetically; (4) persons are created through the unifying activity of self-narrative ; (5) persons are constituted through socio-historical and cultural processes; and (6) the concept of person is a normative ideal . I suggest that it is important to consider all of these projects and related criteria in order to appreciate fully how an entity becomes a human person.