The idea that all the entities in the world may be, for legal and moral purposes, divided into the two categories of ‘persons’ and ‘things’ comes down to us from the tradition of Roman law. In the law, a ‘person’ is essentially the subject of rights and obligations, while a thing may be owned as property. In ethics, a person is an object of respect, to be valued for her own sake, and never to be used as a mere means to an end, while a thing has only a derivative value, and may be used as a means to some person's ends. This bifurcation is unfortunate because it seems to leave us with no alternative but to categorize everything as either a person or a thing. Yet some of the entities that give rise to the most vexing ethical problems are exactly the ones that do not seem to fit comfortably into either category. For various, different, kinds of reasons, it seems inappropriate to categorize a fetus, a non-human animal, the environment, or an object of great beauty, as a person, but neither does it seem right to say of such things that they are to be valued only as means.