Motivation for the Book This book seeks to establish the state of the art in the cyber situational awareness area and to set the course for future research. A multidisciplinary group of leading researchers from cyber security, cognitive science, and decision science areas elab orate on the fundamental challenges facing the research community and identify promising solution paths. Today, when a security incident occurs, the top three questions security admin istrators would ask are in essence: What has happened? Why did it happen? What should I do? Answers to the ?rst two questions form the core of Cyber Situational Awareness. Whether the last question can be satisfactorily answered is greatly de pendent upon the cyber situational awareness capability of an enterprise. A variety of computer and network security research topics (especially some sys tems security topics) belong to or touch the scope of Cyber Situational Awareness. However, the Cyber Situational Awareness capability of an enterprise is still very limited for several reasons: * Inaccurate and incomplete vulnerability analysis, intrusion detection, and foren sics. * Lack of capability to monitor certain microscopic system/attack behavior. * Limited capability to transform/fuse/distill information into cyber intelligence. * Limited capability to handle uncertainty. * Existing system designs are not very friendly to Cyber Situational Awareness.