National biosecurity is a set of practices that regulate how goods, services, and living organisms move through the nation. Of particular interest are bodies that cross borders, be they human, animal, or germ. Microbes cling to other forms of life, including humans, rendering all lifeforms suspect in these borderlands. This chapter explores how nations are made through the management of biological nature, and how containing microbes on the border is a vital act of national security. Today in the borderlands, contemporary cases of food security and swine flu entangle with histories of immigration control practices which were instituted as an act of national care, even as they dehumanized immigrants and naturalized racial discourses about contamination.