Understand the threats: “Global Catastrophic Biological Risks: Toward a Working Definition,” an essay written by the Johns Hopkins Center for Health Security, provides context on how the GHS Index indicators establish measures that can be used to prevent and respond to potential global catastrophic biological risks (GCBRs). Since GCBRs constitute an emerging policy concern and area of practice, the Center invited experts from a variety of disciplines to engage with underlying concepts and assumptions in order to refine collective thinking on GCBRs and thus advance protections against them. The Center was a partner in the creation of the GHS Index.