Participatory sensing is a new research area that emerged from the need to complement our previous efforts in wireless sensor networks. It takes advantage of the emergence of rich-sensor mobile phones and their wide adoption, in order to turn people to producers of sensed data and enable new classes of collective applications. Unavoidably, this raises a lot of privacy concerns, as people are becoming sensors and give out a lot of personal information, like their location. If we choose to protect their privacy by anonymizing the data and completely hiding any identifying information, then the visibility of their contributions to others is lost. However, it is important to maintain this property, in order to support accountability on one hand and allow people gain reputation for their efforts on the other hand. In this book chapter we investigate which of the available technical solutions we need, in order to resolve this conflict and what are the research directions that emerge.