Biosecurity is a concern in many parts of the world but is differently conceived and addressed depending on context. This article draws on two cases concerned with life sciences research involving dangerous pathogens, one in the United States and one in Israel, to examine this variability. In both cases, concern revolves around issues of biosafety and bioterrorism, which are targeted by similar policies and solutions. The cases, nevertheless, differ. In the United States, biosecurity is contextualized in the dynamics between science and society, and apprehension about research with dangerous pathogens focuses on the social risks and benefits of such research. In Israel, biosecurity is contextualized in the dynamics between science and the state and hinges on whether and how far the state should restrict scientific freedom. In view of this difference, the authors advocate the development of a nuanced concept of biosecurity capable of describing and explaining local permutations. They suggest reconceptualizing biosecurity as a boundary object that mediates between competing domains and that takes variable form in efforts to resolve the problem of securing life.