In this article I examine several criticisms of the concept of vulnerability. Rather than rejecting the concept, however, I argue that a sufficiently rich understanding of vulnerability is essential to bioethics. The challenges of international research in developing countries require an understanding of how new vulnerabilities arise from conditions of economic, social and political exclusion. A serious shortcoming of current conceptions of vulnerability in research ethics is the tendency to treat vulnerability as a label fixed on a particular subpopulation. My (...) paper examines the role of this “label” metaphor in current statements of research ethics. In contrast to this prevailing “label” metaphor, my own positive account of vulnerability develops a dynamic way of understanding the structure of the concept of vulnerability based on the idea of “layers of vulnerability.” I examine several cases involving women, as they are sometimes labeled as a vulnerable population and sometimes not. My analysis demonstrates the essential role of this revised concept of vulnerability in bioethics and research ethics. (shrink)