Organizational theorists have long recognized the important role cooperation plays in organizations. However, current theories say little about the antecedents of cooperative behavior in organizations. In this chapter, I present a conceptual framework for analyzing cooperation derived from social identity theory and social categorization theory. According to this framework, people are more likely to cooperate with other members of an organization when their identification with the organization is salient. The framework identifies several psychological processes mediating this link between organizational identification and cooperation, including group-based trust, social attraction, and self-presentational concerns. The framework also describes a number of structural and psychological determinants of organizational identification.