  With the overwhelming online products available in recent years, there is an
increasing need to filter and deliver relevant personalized advice for users.
Recommender systems solve this problem by modeling and predicting individual
preferences for a great variety of items such as movies, books or research
articles. In this chapter, we explore rigorous network-based models that
outperform leading approaches for recommendation. The network models we
consider are based on the explicit assumption that there are groups of
individuals and of items, and that the preferences of an individual for an item
are determined only by their group memberships. The accurate prediction of
individual user preferences over items can be accomplished by different
methodologies, such as Monte Carlo sampling or Expectation-Maximization
methods, the latter resulting in a scalable algorithm which is suitable for
large datasets.
