Methods, systems, and apparatus, including computer programs for identifying, using historical interactions associated with a first user, contact groups, where the first user is associated with each contact group, are provided. A score, with respect to a second user, is calculated for each contact group based on an amount of interaction between the second user and the respective contact group, thereby deriving a plurality of scores. A first contact group is determined. The first contact group has a first score in the plurality of scores that satisfies a predetermined threshold. A contact group suggestion is generated, responsive to the determining, that comprises an invitation to add the second user to the first contact group. The first user is notified of the contact group suggestion.