Ad hoc and sensor networks present unique challenges in the area of security given their lack of a secure infrastructure, dynamic topology and severe resource restraints. The research presented in the six articles comprising this volume cover a variety of topics including trust establishment in Mobile Ad-Hoc Networks (MANETs), security of vehicular ad-hoc networks, secure aggregation in sensor networks, detecting misbehaviors in ad-hoc networks, secure group communication, and distributed signature protocols for ad-hoc networks. "Ad-hoc and sensor networks will become increasingly more important, especially in the areas of military defense and disaster recovery," said Dr. Ning, co-editor. "Security is a big concern in these networks, so researchers are working on developing security systems that provide multiple lines of defense, including detection of physical attacks and compromised nodes." Examples of ad-hoc and sensor networks that are currently being developed are vehicular networks that allow the transmission of traffic information, networks that allow tanks and fighter jets to communicate directly on the battlefield and sensor networks that use multiple sensor nodes to monitor an environment.