Analysts from a range of disciplines (especially sociology and social anthropology) highlight the role of the other' in the construction and de®nition of national identity. Recently some social psychologists have come to emphasize the inherently relational nature of identity. Drawing upon these recent investigations, the present paper reports a ®eld study investigating the context-dependent nature of group identity. Using a modi®ed version of the Katz±Braly task, British subjects (n 240) stereotyped two national groups: Americans and British. They did so in two conditions. In the one-group' conditions, subjects rated either of the two groups. In the two-group' conditions, they rated one whilst also considering the other. Following Oakes, Haslam and Turner (1994) we predicted that whereas subjects' stereotypes of the national outgroup (the Americans) would be unaected by this manipulation, their stereotype of the national ingroup (the British) would be aected. This prediction was con®rmed. We also predicted that the national ingroup stereotype obtained in the two-group' condition would be one which was de®ned in contrast to the American `other' which constituted the comparative context. Using a measure which takes into account the applicability of ingroup-de®ning terms to both the ingroup and the outgroup (the diagnosticity measure of stereotyping proposed by McCauley and Stitt, 1978) we show that the ingroup identity de®nition produced in this condition did indeed dierentiate the British from the Americans. The signi®cance of these data for those concerned with the application of social psychological theory to real-life social problems is discussed.