Composed primarily of the mages of both Dorsine proper and the immediately surrounding area, the Sages’ Guild has branches throughout the Empire (and is rumored to have a couple in other lands; they have no official position on that particular question).
On the whole, the Guild takes itself rather more seriously than it probably should; while its power is not inconsiderable, there are fewer mages than there once were, and the inherent instability of an organization of wizards, sorcerers, and other dabblers in the Arcane Arts leads the guild to spend more of its time wrangling its membership than it would like, leaving less for dealing with outside interests. This likely suits other powers in the city quite well.
For all of its internal issues, the Guild will band together in a heartbeat to protect itself from outside threats1, and in about 3 to protect the Empire. Thus, they currently have a couple of teams investigating the possible causes of the encroaching desert, but have found no conclusive leads thus far.
Most Guild members (about 70%) are wizards, with about 20% sorcerers. The remaining 10% are composed of bards, magi, witches, etc.. In theory, any individual capable of casting even a single Arcane spell (be it as a spell or a supernatural/spell-like ability based on race or class) is welcome to join the Guild; in practice, most Guild events are aimed at those who study Arcana in depth, and those who “dabble” generally feel politely dis-invited to all but the most local of gatherings. (In game-terms, anyone with a caster level of less than about 3 is unlikely to be greeted enthusiastically at any event more important than a mixer, and a caster level of about 8 is necessary for most events beyond the local chapter; that said, the class that grants the caster level is almost completely irrelevant to the welcome, save that wizards tend to be a hair more clique-ey than other classes.)
The Guild runs The Academy, and the Guild’s master also serves as the Academy’s Headmaster. It is not uncommon for Guild-masters to delegate some, even all, of the Headmaster’s duties to an advisor.