Attacks in London, Madrid, Bali, Oklahoma City and other places indicate that improvised explosive devices (IEDs) are among the weapons of choice of terrorists throughout the world. Scientists and engineers have developed various technologies that have been used to counter individual IED attacks, but events in Iraq and elsewhere indicate that the effectiveness of IEDs as weapons of asymmetric warfare remains. The Office of Naval Research has asked The National Research Council to examine the current state of knowledge and practice in the prevention, detection, and mitigation of the effects of IEDs and make recommendations for avenues of research toward the goal of making these devices an ineffective tool of asymmetric warfare. The book includes recommendations such as identifying the most important and most vulnerable elements in the chain of events leading up to an IED attack, determining how resources can be controlled in order to prevent the construction of IEDs, new analytical methods and data modeling to predict the ever-changing behavior of insurgents/terrorists, a deeper understanding of social divisions in societies, enhanced capabilities for persistent surveillance, and improved IED detection capabilities.