Reputation management is a powerful security tool that helps establish the trustworthiness of users in online applications. One of the most successful use of reputation systems is in e-commerce web sites such as eBay.com and Amazon.com which use reputation systems to root out fraudulent sellers. Reputation systems can also play an important role in social networks to enforce various security requirements. For example, a reputation system can help filter fake user profiles. However, a major challenge in developing reputation systems for social networks is that users often hesitate to publicly rate fellow users or friends due to the fear of retaliation. This trend prevents a reputation system from accurately computing reputation scores. Privacy preserving reputation systems hide the individual ratings of users about others and only reveal the aggregated community reputation score thus allowing users to rate without the fear of retaliation. In this chapter, we describe privacy preserving reputation management in social networks and the associated challenges. In particular we will look at privacy preserving reputation management in decentralized social networks, where there is no central authority or trusted third parties, thus making the task of preserving privacy particularly challenging.