From Dragon Eye Atlas
Unlike the Fighters' and Adventurers' Guild, the Mages' Guild has never really been one organisation. Too much ego, presumably. However, the cooperation between the various guilds has become so close over the years that most outsiders now consider them simply different branches of the same guild.
The influence and presence of the Mages' Guild(s) varies widely by region. While in Palan it is essentially a branch of the government, in Schap it is an illegal underground organisation and in Biesen there is only one official chapterhouse, in the capital, under strict controls of the government. In most other realms, the guild functions more or less normally, but in many places it is the most rare and small guild.