This volume explores the connections between Thomas Aquinas’ doctrine of natural law and contemporary social thought. It aims to make explicit the basic notions of Thomas Aquinas's social ontology and to show how key concepts from sociology, economics, and political science relate to his ethics and social thought. Social ontology is a growing area of contemporary social theory. Scholars in this area reflect on the ontological status of society and the various realities that make up the social realm. However, Aquinas scholars rarely use the term social ontology, instead resorting to his natural law to examine social life. This volume argues that the social thought of Thomas Aquinas, including his natural law theory, implies a social ontology. Aquinas adopts a clear position on the ontological uniqueness of human beings, the intentional structure of human action, and the existence of informal social relations and institutional realities that shape human society. This volume shows how these views can be reconstructed into a coherent social ontology. Its chapters are divided into five thematic parts. Part 1 offers conceptual elements to bridge the gap between Aquinas and contemporary social theory. Part 2 considers the metaphysics and theology implicit in Aquinas’ social ontology. Part 3 focuses on the way this ontology is at work in his account of the common good and his approach to natural law. Part 4 expands this reflection to economics. Finally, Part 5 addresses legal and political issues such as political polarization, family law, and the ethics of war. Aquinas, Natural Law, and Social Ontology will appeal to scholars and graduate students interested in the thought of Thomas Aquinas, social and political philosophy, contemporary social theory, Catholic theology, and the social sciences.