The war on terror's emphasis on denying sanctuary and safe havens to terrorists has placed a premium on physical territory, from mountain caves and frontier hideouts to the bordered world of modern states. Denial of Sanctuary highlights the limits of conventional thinking on the subject, and suggests new approaches to understanding this complex and misunderstood feature of modern conflict. Critics of the war on terror have pointed to the futility of waging war on a tactic. Its emphasis on denying sanctuary and safe havens to terrorists, rooted primarily in traditional counterinsurgency theory and poorly conceptualized policy statements, has placed a premium on physical territory, from mountain caves and frontier hideouts to the bordered world of modern states. To fully understand sanctuaries is to uncover the problems and pitfalls of waging war on locations—exposing the secret lives of multiple hidden worlds, filled with extremists, criminals, soldiers, and spies, with the pious and the profane, with dangers that lie below the surface and in the margins. As this volume makes abundantly clear, such a murky underground is far more complex and varied than the conventional wisdom suggests. Terrorists have hidden in plain sight in modern cities, used advanced communications technology to build virtual refuges, crafted militant enclaves out of the disarray of failed states, flocked to distinctly unsafe insurgent battlespaces, and generally challenged the protective limits of law, citizenship, and state. Denial of Sanctuary brings together top experts in the field to expand the debate; to explore the roots, causes and consequences of the problem; and to clarify our understanding of sanctuary in terrorist thought and practice.