All the clan societies remain autonomous, being linked formally only by a shared allegiance to the chief; though working informally together - and in association with the Clan Centre in Scotland - to further their common interest in the worldwide clan.

Representatives of all the existing clan bodies - often called "Elders" - meet from time to time to discuss how best to do this; and at a "Conclave" in 2000 they agreed on this declaration:

The mission of each Clan MacMillan organization is to be part of the world-wide family (by birth, marriage, adoption, or interest), loyal to our Chief and supportive of the Clan Centre, researching, communicating, and celebrating the story and heritage of Clan MacMillan. We seek to work among ourselves and with others in the spirit of our motto: Miseris succurrere disco.