Ungoverned territories-failed or failing states or ungoverned areas within otherwise viable states-generate all manner of security problems and can become terrorist sanctuaries. Using a two-tiered framework areas applied to eight case studies from around the globe, the authors seek to understand the conditions that give rise to ungoverned territories and what makes some ungoverned territories more conducive to a terrorist or insurgent presence than others. On the basis of this ground-breaking analytical work, they identify three types of ungoverned territories and their effects on U.S. security interests and develop strategies to improve the U.S. ability to mitigate these effects.