MANET formed by collection of mobile nodes, characterized by nonexistence of physical infrastructure, It's getting popular day by day, due to wide use of mobile and handheld devices. Topology of this network changes dynamically with randomly moving nodes. Therefore routing protocols play a prominent role in setting up efficient route among pair of nodes. Many proactive, reactive & hybrid routing protocols have been proposed, Out of which one of well known is AODV due to its high performance gain. Cooperative nature of nodes exposes MANET to various kinds of passive & active attacks. Sinkhole is one of severe kind of attack which attempts to attract most of network traffic towards it & degrade performance of network. AODV is mainly analyzed under attacks as blakhole, wormhole & flooding. It needs to analyze under other kinds of attack also. This book mainly focuses on sinkhole problem, & its consequences on AODV based MANET in the form of simulation results obtained using widely use network simulator NS2 by considering various performance metrics, as PDR, Throghput, End to End Delay & packet loss.