Selections of content sources are received. Content source bundles are generated from the selected content sources, each content source bundle defined by one or more selected content sources assigned to that content source bundle, and each content source bundle having associated data indicative of users interested in content provided by the selected content sources of that content source bundle. The content source bundles are presented for use in advertising campaigns in which advertisements can be published on selected content sources of a content source bundle, and the performance of each content source bundle used in advertisement campaigns are measured.