Passively populating a list of participants of an electronic communications system includes maintaining a participant list of users of an electronic communications system to be used by a user of the electronic communications system. Existing users of the electronic communications system that are known to the user are identified, and communications strengths between the user and each of the identified existing users are determined. The identified existing users with the highest communications strengths are designated for addition to the participant list. An existing group or a newly created group within the participant list to which each of the designated users should be added may be identified.