This paper addresses the question: Who or what can have a moral status in the sense that we have direct moral duties to them? It argues for a biocentric answer which ascribes inherent moral status value to all individual living organisms. This position must be defended against an anthropocentric position. The argument from marginal cases propounded by Tom Regan and Peter Singer for this purpose is criticised as defective, and a different argument is proposed. The biocentric position developed here is related to that of Albert Schweitzer and Paul F. Taylor, but rejects their assumption of equal inherent value for all living organisms. It argues instead for equal moral status value for moral persons and agents, and gradual moral status value for nonpersons, depending on their degree of similarity with moral persons. Mary Ann Warren's recent book on Moral Status is also discussed. The argument is constructed as a casuistic argument, proceeding by analogical extension from persons to nonpersons. The meta-ethical question of its pragmatic validity is discussed.