Abstract: Group fissions occur when two or more members leave a parent group to either form a new group or join an existing group. This article investigates the interplay between two factors: the presence of an intragroup conflict and subgroup boundaries on the group fission process. It is hypothesized that subgroup divisions act as potential fault lines along which groups split after they experience conflict. The results of three experiments, one scenario study and two laboratory studies involving small task groups, support the group fault line hypothesis. The authors discuss the implications of these findings for theory and research on membership changes in small groups.