Chapter Two relies on extensive research from the fields of psychology and political science to establish that polarization is a deep-seated feature of the American condition. Ideological polarization stymies our efforts to reach common ground. Americans are polarized by more than ideology, though, and affective polarization may in fact be more consequential. Research shows that group membership drives human behavior, and, as our social identities increasingly align with a particular political identity, our sense of political affiliation defines our sense of self. The pull of group membership is powerful enough to subvert our ideological inclinations—tribal loyalty can be more compelling than principles. Partisan antipathy is on the rise, causing us to malign, mistrust, and even punish the political other. The chapter concludes by summarizing the challenge for educators: polarization is a chronic condition, and it awaits our students.