Entries within a participant list of an electronic communications system may be categorized automatically into one or more groups based on attributes of users represented in the participant list. Categorizing users includes maintaining a list of identifiers that are selected by a first user and for which online presence information is made perceivable through the list. The list includes one or more categories into which the identifiers are categorized. At least one attribute associated with an identifier for which online presence information is to be made perceivable through the list and attributes stored relative to at least one of the categories are accessed. The attributes associated with the identifier are compared to the stored attributes. Based on results of the comparison, at least one category within the list that corresponds to the identifier is identified, and the identifier is categorized into the identified category.