This research addresses the strength of the homeland security policy regime that was constructed after the terrorist attacks of September 2001. We argue that homeland security provides a preeminent example of the challenges of developing policy regimes that focus policymaking on a common goal across diverse subsystems. All the ingredients for fashioning a powerful regime were in place after the terrorist attacks of September 2001—a common purpose, engaged stakeholders, and institutional redesign. But for a variety of reasons that we discuss, the results are far from cohesive. The lessons we draw are more general ones regarding factors that influence the strength of boundary-spanning policy regimes.