The Mage Guild
Current Guild Leader: Darius King
The Mage Guild is loose organization of all the Mages in the Atlanta area. Like the Invictus (for vampires), everyone is assumed to belong to the Mage Guild, dues paid or not, active in guild activities or not. Only if a person specifically chooses to opt-out does one lose the benefits and protections of the Mage Guild, and most people would never even think of doing that.
The Mage Guild not only exists as a resource to aid in the training of young mages and a research avenue for its more inspired members, but as a layer of protection over all of its members against issues involving the interaction of the other super natural beings in the city.
The vampires, in particular, seem to cause the most problems for the Mage Guild members, intentionally or no.