In this discussion of papers by Doise (1988) and Tajfel (1982) it is argued that a conceptual distinction should be made between social groups and social categories. A social group can be considered as a ‘dynamic whole’ or social system, characterized by the perceived interdependence among its members, whereas a social category can be defined as a collection of individuals who share at least one attribute in common. This distinction is crucial for the understanding of outgroup favouritism in the minimal intergroup situation, the basic similarity between large scale groupings and face-to-face groups, the difference between group identification and social identity and the issue of categorizations versus attributions in intergroup conflict.