Relations between groups of people are determined both by the attitudes and behaviour patterns of the individuals who constitute these groups, and by their social, economic, political and ideological background. Intergroup relations are therefore open to both psychological and sociological explanations, and the study of intergroup relations represents a way in which these two levels of explanation, which so often fail to take account of each other, may be integrated. This is the thesis advanced here by Willem Doise. Professor Doise discusses psychological explanations of social stereotypes and prejudices by examining specific clinical psychologists and then approaches these phenomena sociologically. He also describes the psychological process of category differentiation and its role in intergroup relations. This book, first published in 1978, will be of particular interest to social psychologists, and to all social scientists interested in the problem of integrating psychological and sociological explanation.