Introduction Crafting a global strategy to address threats presented by biological weapons or the emergence of virulent infectious diseases requires the involvement of many disciplines, ranging from microbiology to law enforcement. The global network required for such integrated policy has profound implications for the role law plays in efforts to improve biosecurity. Few, if any, proponents of strengthening biosecurity assert that governments, international organizations, and non-state actors should pursue this objective outside the bounds of the law. Some opponents of actions taken to address biosecurity argue that such actions threaten the rule of law. At the same time, merely creating more law is not a sufficient response to biosecurity threats. Fostering better approaches to biosecurity requires an understanding of the changing functions of law in this policy realm, and this chapter focuses on this task. Analyzing the role of law in the contemporary biosecurity context reveals changes and challenges that have pushed countries, individually and collectively, toward common legal strategies. These strategies stimulate the development of a harmonizing jurisprudence on the role of law in addressing disease threats, or the emergence of a shared ius pestilentiae. This “law of disease,” and its global scope, constitutes a critical element of the architecture of the networked global approach to biosecurity analyzed in this book. The development of this ius pestilentiae represents a recent and radical departure from previous domestic and international legal realities in the areas of biological weapons and public health. The newness of the ius pestilenitae means that we must understand both the need for transformed legal strategies and the gap between having this understanding and achieving biosecurity under the rule of law.