The years since the devastating attacks of September 11, 2001, have seen dramatic developments in the recognized challenges to U.S. national security and in the ways the United States reacts to terrorist threats. Those reactions have demonstrated both the flexibility and limitations of U.S. criminal law in its ability to adapt to terrorism. A focus on the perceived limitations of U.S. criminal law in this regard has led to calls from key players within the U.S. national security apparatus for an improved regime of investigative detention, such as those currently in place in the United Kingdom and France. But what do the laws of those countries permit that U.S. law does not? What aspects of U.S. criminal law―if any―set it on unequal footing with its European counterparts? What desirable aspects of those systems in the United Kingdom and France are needed and capable of implementation in the United States?