On what basis do people form their social identities? To investigate this issue, the present research investigates cross-cultural differences in self-stereotyping, a key outcome of social identification. In particular, the research tests the hypothesis that ingroup ties are a stronger predictor of self-stereotyping among people from individualist cultures than among people from collectivist cultures. In Study 1, university students (N = 117) completed measures of ingroup ties and self-stereotyping with respect to an intimacy group (family and friends). Consistent with predictions, ingroup ties significantly predicted self-stereotyping among individualists but not among collectivists. Study 2 (N = 104) found a similar pattern of results among members of the global internet community who considered either an intimacy group (their friends), a task group (their work group) or a social category (their gender). These results indicate that people in individualist cultures are more likely than those in collectivist cultures to base their social identities on ingroup ties. The implications of these results are discussed in relation to self-categorization theory's depersonalization account of social identification.