This research examined reasons for the frequently obtained finding that members of numerically minority groups exhibit greater intergroup discrimination than members of majority groups and also sought to determine the conditions under which members of both majority and minority groups exhibit intergroup discrimination. Experiment I examined the role of group identification and found that discrimination by members of a majority group was equivalent to that of minority group members when identification was experimentally induced. Experiments 2 and 3 examined further the underlying bases for minority and majority discrimination. Consistent with predictions derived from optimal distinctiveness theory (Brewer, 1991), identification with the in-group was found to be a necessary condition underlying intergroup discrimination, but motivations for discrimination varied as a function of satisfaction with in-group size and distinctiveness. (C) 2001 Academic Press.