In the post-9/11 era, a new focus on failing states and their ability to threaten global security has influenced US foreign policy and aid policy. This paper explores the links between failing states and transnational threats such as terrorism, weapons proliferation, organized crime, and global pandemics. It argues that analysts and policymakers must look more deeply at precisely how failing states pose a threat to global security. By offering a thorough survey of this issue, the author provides a framework for determining which states are associated with which dangers. He puts forth a roadmap for US policy that includes deeper intelligence collection and analysis, improved policy coherence, and more robust international engagement to tackle the threats posed by weak states in the new millennium. This paper is a part of CGD’s ongoing work on security and development.