Providing a description of the evolving terrorist threat, this book’s goal is to compare the underlying risk of attack to the architecture of financial protection that has been facilitated by the Terrorism Risk Insurance Act (TRIA). The Terrorism Risk Insurance Act (TRIA) requires insurers to offer commercial insurance that will pay on claims that occur from a terrorist attack, and for losses on the scale of 9/11, TRIA provides a backstop in the form of free reinsurance. The authors describe the evolving terrorist threat with the goal of comparing the underlying risk of attack to the architecture of financial protection that has been facilitated by TRIA.