The dynamic and cooperative nature of ad hoc networks present substantial challenges in securing these networks. There is a natural incentive for nodes to only consume, but not contribute to the services of the system. Intentional misbehavior can aim at an advantage for the misbehaving node or just constitute vandalism, such as enabling a malicious node to mount an attack or a selfish node to save power. The use of reputation systems in many different areas of IT is increasing because of their widely publicized use in online auctions and product reviews. Reputation systems are used to decide who to trust, and to encourage trustworthy behavior. In this paper we introduce the concept, goals, features and architecture of reputation systems and survey the reputation and trust based security schemes that were proposed for ad hoc networks. Finally we conclude this paper.