Methods, systems, and apparatus, including computer programs encoded on a computer-readable storage medium, and including a method for providing advertisements. The method comprises determining at least in part based on analysis of user interaction data of a plurality of users in a user network, an inferred group of users that interact together, including two or more users from the users in the user network. The method further comprises receiving a request to present an advertisement to each of two or more users of a group of users that interact together, and based at least in part on the received request, providing for display, to each of two or more of the users in the inferred group of users that interact together, the requested advertisement.