During social interactions in daily life, people possess imperfect knowledge of their interdependence (i.e., how behaviors affect each person’s outcomes), and what people infer about their interdependence can shape their behaviors. I will discuss theory and research that suggests people can infer their interdependence with others along several dimensions, including mutual dependence, power, and corresponding-versus-conflicting interests. I will discuss how perceptions of interdependence affect how people cooperate and punish others’ defection in everyday life.