We address the issue of misbehavior detection and reaction in IEEE 802.11 based Ad Hoc networks. Selfish misbehavior involves disobeying standard protocol mechanisms to gain unfair access to the channel at the expense of other users. We outline conditions on genuine (non-misbehaving) node's throughput to guarantee the presence of misbehavior, and propose non-adaptive and strong reaction mechanism for such aggressive misbehaviors. For selfish misbehaviors which do not result in severe throughput degradation for genuine users, we design an adaptive reaction mechanism. Both mechanisms are distributed in nature, rely only upon local information available at genuine nodes, and are thus easily implementable in practice. Proposed reaction mechanisms provide the necessary disincentive towards selfish misbehavior, and are aimed at preventing misbehavior.