Throughout evolutionary history, intergroup competition has been an influential part of social life. Although the topic has received substantial empirical attention among social psychologists, the majority of that work has focused on how ingroup and outgroup members regard one another. Only recently have researchers begun examining how intergroup rivalry changes that way that ingroup members perceive and relate to one another. New findings suggest that a variety of within-group processes are influenced by the presence of a rival outgroup. In general, altruistic cooperation and prosocial motives increase among ingroup members when their group competes against another. The relationship between leaders and followers also shifts in response to intergroup rivalry: rather than wielding their power for selfish purposes, leaders prioritize the needs of their group. On the flip side, followers’ choice of leader changes, preferring males during times of intergroup competition but females in the absence of competition. Given the substantial impact of intergroup competition on ingroup processes, future research should continue to deepen the field’s knowledge of this topic. Additionally, the scope of research should be broadened to capture the effect of intergroup competition on ingroup dynamics, such as performance and group outcomes.