Group-based emotions are experienced as a result of group categorization and group identification. We first review the transformative idea that emotion can occur as a group-level phenomenon driven by group-level processes. We then briefly review the impact of this idea on research about intragroup processes and intergroup relations in the decades since 1998. We conclude by raising some questions whose answers would further extend the reach and predictive power of group-based emotions in both intragroup and intergroup contexts.