Most existent protocols, applications and services for mobile Adhoc networks (MANETs) assume a cooperative and friendly network environment and do not accommodate security. In MANETs, intrusion prevention (IPS) and intrusion detection (IDS) techniques need to complement each other to guarantee a highly secure environment. The IPS and IDS play different roles in different states of the network. Intrusion prevention measures, such as encryption and authentication, are more useful in preventing outside attacks. Once the node is compromised, intrusion prevention measures will have a little effect in protecting the network. Therefore, an intrusion detection system is serving as the second line of defense in Adhoc network. This Book used the incremental approach to designing the detection engine for Adhoc network environments.