This book, Critical Infrastructure Protection IV, is the fourth volume in the annual series produced by IFIP Working Group 11.10 on Critical Infr- tructure Protection, an active international community of scientists, engineers, practitioners and policy makers dedicated to advancing research, development and implementation e?orts related to critical infrastructure protection. The book presents original research results and innovative applications in the area of infrastructure protection. Also, it highlights the importance of weaving s- ence, technology and policy in crafting sophisticated, yet practical, solutions that will help secure information, computer and network assets in the various critical infrastructure sectors. This volume contains seventeen edited papers from the Fourth Annual IFIP Working Group 11.10 International Conference on Critical Infrastructure P- tection, held at the National Defense University, Washington, DC, March 15?