MANET is a continuously self-configuring, decentralized, infra structure less network of mobile nodes connected without wires. MANETs are characterized by dynamictopology change, high mobility and limited resources. Due to the wireless and infrastructure less nature of MANET, they are more vulnerable to various threats. The primary requirement in MANET is the cooperation of all the nodes in the network for the efficient communication. If there is a malicious node which is not cooperating in the network may lead to false route which is a serious security concern. Hence the misbehaving nodes need to be isolated from the network in order to enhance efficient routing. This paper reviews various approaches to detect and isolate malicious nodes in MANET. © 2010 RJPBCS.