Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for annotating search results. In one aspect, a method includes receiving a search query from a user, the user having a plurality of social affinity groups, each social affinity group identifying a group of users and the user as a proper subset of users of a network. The method includes receiving search results responsive to the search query, each search result referencing a resource. The method includes identifying a search result referencing a resource having an association with one or more of the social affinity groups. The method includes annotating the search result, the annotation describing the association of one of the social affinity groups with the resource, and further identifying the social affinity group. The method includes presenting the annotated search result to the user.