 There seems to be little prospect for consensus on the moral status of people with the most severe cognitive disabilities. There are sharp disagreements about how, or even whether, the moral status of humans can be grounded, and about the weight to be given our strongest and most considered, moral convictions. Accounts that ground full moral status in an individual’s possession of psychological attributes inevitably exclude some portion of humanity, and appear to have implications for the treatment of the excluded human beings that few of us are willing to accept. Those implications are avoided by accounts that ground full moral status in our species membership—in the nature of the species or in our biological relationships to other members. Those implications are also avoided by accounts that deny the need to ground the moral status of human beings in any attribute we or our group possesses. But these ways of avoiding exclusion have significant costs. They require a strong partiality toward those with shared biological features, physical appearances, or origins, a partiality that conflicts with equally strong, if more abstract convictions about the justification for our conduct towards others. And they leave deep uncertainty about the moral constraints on our treatment of other living beings and about the boundaries of humanity itself.