The moral status of a being is the condition conferring moral considerability and (possibly) moral rights to such a being. There has been a wide philosophical debate about the basis upon which moral status should be attributed and the kinds of beings to which it should be granted. There are three main questions regarding the notion of moral status: What does it mean for a subject to have a moral status? On which basis should it be attributed? To which subjects should it be recognized (persons, "marginal" human beings, animals, chimeras) ? In this paper I examine the different responses that moral individualism, the species-based theories, the relational theories and contractualism have provided to these questions.