This study examines beliefs about the ontological status of social categories, asking whether their members are understood to share fixed, inhering essences or natures. Forty social categories were rated on nine elements of essentialism. These elements formed two independent dimensions, representing the degrees to which categories are understood as natural kinds and as coherent entities with inhering cores ('entitativity' or reification), respectively. Reification was negatively associated with categories' evaluative status, especially among those categories understood to be natural kinds. Essentialism is not a unitary syndrome of social beliefs, and is not monolithically associated with devaluation and prejudice, but it illuminates several aspects of social categorization.