What makes persons persons? In order to give an answer to this fundamental question, the article refers to central aspects of the concept of ‘person’. First, it takes the history of the concept into account, from its origins in Antiquity. Our understanding of persons is not based so much on the mask of ancient theatre but on the grammatical sense of ‘persons’ as mediated by patristical speculation on the Trinity. Then, regarding the modern debate on personal identity, it argues against John Locke and Derek Parfit that personal identity is not qualitative but numerical. In opposition to Peter Singer’s argument of Speciesism, the author maintains that belonging to the human species is a sufficient condition for the status of personhood. Finally, he defends for the thesis also held by Kant that if there is at all a rationally justifiable moment of the person’s coming to be, then that is the moment of conception.