The evolution of United Nations treaties in the domain of public health over the last two decades is one of the most significant developments in public international law. Although public health is one of the earliest fields of international legal cooperation and one of the first domains in which an intergovernmental organization was created, the scope of international legal cooperation in public health was, until recently, highly limited. This chapter provides an overview of the contribution of United Nations treaties in the evolving field of international health law. It examines the historical origins and the factors contributing to its contemporary evolution. In addition, the chapter briefly reviews the contribution of UN organizations, especially the World Health Organization, to the codification efforts in this realm.