Research on the perception of entitativity addresses the question, “How do we come to see a collection of people as a group?” Entitativity is the degree to which groups are perceived as having the nature of an entity. Thus the perception of entitativity lies at the core of a wide variety of processes that involve groups. It is connected to numerous important processes in intergroup perception and in intergroup relations. This entry distinguishes entitativity from another important group feature, similarity, and discusses the consequences of entitativity for information processing, stereotype formation, collective responsibility, and social identity.