This article describes the historical emergence of vital systems security, analyzing it as a significant mutation in biopolitical modernity. The story begins in the early 20th century, when planners and policy-makers recognized the increasing dependence of collective life on interlinked systems such as transportation, electricity, and water. Over the following decades, new security mechanisms were invented to mitigate the vulnerability of these vital systems. While these techniques were initially developed as part of Cold War preparedness for nuclear war, they eventually migrated to domains beyond national security to address a range of anticipated emergencies, such as large-scale natural disasters, pandemic disease outbreaks, and disruptions of critical infrastructure. In these various contexts, vital systems security operates as a form of reflexive biopolitics, managing risks that have arisen as the result of modernization processes. This analysis sheds new light on current discussions of the government of emergency and ‘states of exception’. Vital systems security does not require recourse to extraordinary executive powers. Rather, as an anticipatory technology for mitigating vulnerabilities and closing gaps in preparedness, it provides a ready-to-hand toolkit for administering emergencies as a normal part of constitutional government.