Although there has been much work done in the industry and academia on developing the theory and application of social networks as well as recommender systems, the relation between these research areas is still unclear. An innovative idea, which enables to integrate these areas, and applies recommendation systems to the online social network systems, is presented in this book. Recommender systems for social networks differ from the typical kinds of recommendation solutions, since they suggest human beings to other ones rather than inanimate goods. Thus, conventional recommendation methods should be enhanced by social features of the networks and their members. This book describes the results arising from the study on the recommendation framework for virtual communities. It also contains an overview of recent approaches to recommender systems and social networks, as well as description of the online social network systems.