This paper is in two parts, both of which are concerned to explore the justificatory presuppositions and limits of the idea of a universal framework for bioethical judgments; a global bioethics. The first part takes up the issues of the meaning and justification of global bioethics. After distinguishing the different ways in which global bioethics may be understood, various strategies for justifying the project are described. It is argued that in the absence of an actual global consensus on the content of the framework, a procedure for establishing what that content should be is required. This requirement is explored by outlining the contributions of Hermeneutics and Critical Theory. This part of the paper concludes with the view that one central presupposition of the project of global bioethics is that there is, or could be, a global consensus about the general norms of reason and discourse that disagreements over the ethical content of the framework should observe. Part two of the paper aims to explore one aspect of the rational limit to global bioethics that is revealed by the interplay between it and the claims of collective identity that groups of people make. The paper concludes that because of its ‘existential connotations' identity may be resistant to rational scrutiny, which paradoxically may not be irrational. Those for whom the ‘language of identity' gives way to the ‘language of interests' may well be able to engage in compromise and negotiation towards consensus on ethical principles and values.