Group faultlines are hypothetical dividing lines that may split a group into subgroups based on one or more attributes. An example of a strong faultline is a group of two young female Asians and two senior male Caucasians. Members’ alignment of age, sex, and ethnicity facilitates the formation of two homogeneous subgroups. On the other hand, when a group consists of a young female Asian, a young male Caucasian, a senior female Caucasian, and a senior male Asian, the group faultline is considered weak because subgroups, regardless of how they are formed, are diverse. As a relatively new form of group compositional pattern, the group faultline is associated with subgroup formation, and these subgroups, rather than the whole group, can easily become the focus of attention. When members strive to obtain more resources and protect their subgroups, between-subgroup conflict, behavioral disintegration, lack of trust, lack of willingness to share information, and communication challenges are likely. As a result, group performance is often negatively affected, and sometimes groups may even be dissolved. These results were repeatedly found in studies of experimental groups, ad-hoc project groups, organizational teams, top management teams, global virtual teams, family businesses, international joint ventures, and strategic alliances.