A social networking system allows users to create and join groups in the social networking system, in which each group is associated with one or more interests shared by members of the group. To select content for presentation to a viewing user of the social networking system who is a member of a group, the social networking system may determine one or more topics associated with the group based at least in part on a classification system and on information associated with objects maintained in the social networking system that are similar to the group. The topic(s) associated with the group also may be determined based on information associated with the group, with members of the group, and/or with objects associated with the group. The social networking system may then select one or more content items associated with the topic(s) for presentation to the viewing user via a group page.