The concept of the person has come to be intimately connected with questions about the value of life. It is applied to those sorts of beings who have some special value or moral importance and where we need to prioritize the needs or claims of different sorts of individuals. "Person" is a concept designating individuals like us in some important respects, but possibly including individuals who are very unlike us in other respects. What are these respects and why are they important? This paper sets out to answer these questions and to develop a coherent and useful concept of the person.