Social communities, whether online or real, can be seen as networks. In these networks, each node corresponds to an individual and two nodes are connected on this network if they are related (e.g. are friends). Social networks are the environment where the social influence takes place. For example, a person is clearly influenced by its neighbors (friends) on a social network about which movie to watch, which video content to post on Facebook, or what to retweet. Or, a rumor will spread among people through the links of this social network.