The fusion of basic ideas in mathematics, biology, and chemistry with ongoing improvements in hardware and computation offers the promise of much more sophisticated and accurate sensing capabilities than currently exist. Coupled with the dramatic rise in the need for surveillance in innumerable aspects of our daily lives brought about by hostile acts deemed unimaginable only a few short years ago, the time is ripe for scientists in the diverse areas of sensing and security to join together in a concerted effort to combat the new brands of terrorism. The contents of this volume can be divided into three broadly defined but interrelated areas: The increasing need for fast and accurate sensing what is the threat; The scientific underpinnings of the ongoing revolution in sensing; Specific sensing algorithms and techniques. A deep understanding of these three topics, and of their interdependency, is clearly crucial to meet the increasing sophistication of those who wish to do us harm. The contributors to this volume are many of the world's leading experts in the development of new methodologies to both comprehend and predict these threats and to effectively deal with them.