Over the last decade, a growing number of public administration theorists have taken up the question of how ontology—assumptions about the nature of existence—shapes our understanding of governance. This substantially updated primer, originally published in Public Administration Review, introduces the essay, provides a basic explanation of ontology, describes the fundamental debates in philosophies of ontology, and discusses why ontology is important to social and political theory and therefore public administration theory and practice. Using an ideal-type approach grounded in differing ontological assumptions, a Governance Typology is provided to support analysis of differing public administration theories. An integrative approach to governance is offered that is grounded in relational process ontology—a foundation that may support a viable synthesis of the other four primary ideal-types. The essay concludes with a call for personal reflection on the part of scholars and practitioners regarding their own ontological commitments and an invitation to collaborative inquiry.