Social ontology examines the fundamental nature of the social world, asking how entities such as institutions, norms, and practices come into being and persist through human thought, language, and interaction. This entry traces major approaches to social ontology from classical philosophy through modern and poststructuralist debates, highlighting their significance for psychology. Early social contract theories emphasized individuals as the foundation of society, influencing behaviorist and cognitive traditions. In contrast, Hegel, Marx, and Durkheim reframed social reality as irreducible to individuals, foregrounding social structures, recognition, and material conditions. Vygotsky, Luria, and Leontiev extended these insights into psychology, developing activity theory to link consciousness with socially mediated practices. Poststructuralist thinkers such as Foucault and Butler challenged the stability of social categories, emphasizing discourse, power, and contingency. Contemporary psychology continues to navigate tensions between individualistic, societal, and poststructuralist ontologies, offering opportunities for pluralism, methodological innovation, and ethically engaged practice.