What does it mean to identify with a social group? Are individuals’ group attachments tied to material or nonmaterial payoffs? What is the existing evidence for social identification due to nonmaterial payoffs? When do identities matter and for what sorts of behaviors? We highlight findings from several literatures in political science, ranging from voting and redistribution to violence and conflict, focusing on nonmaterial, identity-based motivations for behavior in these domains. Doing so allows us to draw out commonalities across research areas that are often held in isolation from one another and that frequently employ overlapping terminology. We summarize important findings and identify open questions; these questions include what the role played by elites is in shaping mass mobilization around identities and what the relationship is between social identities and social norms.