Abstract: This article offers a historical and methodological perspective on the concept of rationality. It gives an overview of the various interpretations of the notion, from self-interest to rational choice and expected utility to strategic rationality and rational expectations. It pays special attention to the ethical dimensions of the concept. The article further places rationality within a long-ranging discussion concerning the status of assumptions within economics. It explicitly considers efforts to test rationality directly. The article concludes with an evaluation of recent efforts to replace rationality with the notion of bounded rationality.