What makes me the same person today that I was yesterday or will be tomorrow? In Plato's Symposium, Socrates observed that all of us are constantly undergoing change--physical as well as changes in our manners, customs, opinions, desires, pleasures, pains, and] fears. Aristotle theorized that some underlying substratum remains constant even while we undergo these changes. John Locke rejected Aristotle's view and reformulated the problem of personal identity in his own way. These essays--written by prominent philosophers and legal and economic theorists--offer valuable insights into the nature of personal identity and its implications for morality and public policy.