The disproportionate impact of risk, hazards, and disasters on socially differentiated groups has been part of the broader disasters research field for over half a century now. As a concept, social vulnerability transcends many social science disciplines but remains firmly grounded in social and spatial inequality processes and outcomes. The variability in space and the peculiarity of places has driven the development of empirically based measurements of social vulnerability, especially in the United States. This article takes a retrospective view of the concept of social vulnerability in tracing origins in hazard and disasters research, its quantification, and its operational use for emergency preparedness, response, recovery, and mitigation. It uses the Social Vulnerability Index (or SoVI) given its intellectual antecedents in the geographical sciences and widespread acceptance within hazards and disasters research as the model. In the brief period since its development twenty years ago, SoVI has moved from a place-based conceptualization to an oft-used method for highlighting inequities in potential hazard impacts and likely recovery from them in both research and practice. More significantly, the history of SoVI and its application illustrates the arc of theory-to-practice, use-inspired geographical scholarship, starting with the idea and witnessing its translation to an operational tool in hazards and disasters policy. Lessons learned and future needs, uses, and improvements in social vulnerability metrics conclude the article.