The aim of this study is to show that, when examining social identification, it is both possible and important to distinguish between self-categorisation, commitment to the group, and group self-esteem, as related but separate aspects of group members' social identity. This was demonstrated in an experiment (N=119), in which Ingroup Status (high/low), Ingroup Size (majority/minority), and Group Formation (self-selected/assigned group membership) were manipulated orthogonally. The results of this study confirm that these three aspects of social identity can be distinguished as separate factors in a principal components analysis. Furthermore, as predicted, the three aspects are differentially related to manipulated group features, as well as displays of ingroup favouritism. Group members' self-categorisations were only affected by the relative size of the group, while group self-esteem was only influenced by group status. Affective commitment to the group depended both on group status and on the group assignment criterion. Importantly, only the group commitment aspect of social identity mediated displays of ingroup favouritism. Copyright © 1999 John Wiley & Sons, Ltd.