Global Virtual Teams (GVTs) ? teams with geographically and temporally dispersed members who heavily rely on computer-mediated communications (CMC) ? face significant collaboration challenges associated with cultural diversity. From the social identity perspective, we investigated the impact of GVT members' cultural individualism/collectivism (I/C) and language identities on their participation in team collaboration. A field experiment involving 33 GVTs was conducted to test our hypotheses. The results indicated that when a team's identity faultlines are strong, its members' I/C and Language identities have significant impact on their levels and forms of participation; and that communication media have significant interaction effects on these relationships.