From Dragon Eye Atlas
Craftsmen and other trades are organized into guilds. There are also guilds for classes, which provide their members with various advantages. In addition to guilds, there are also organised religions and non-religious institutes, all of which can provide characters with knowledge and ressources.
Craftsman guilds are always localized in nature, and the tailors’ guild of one city has little in common with that of the next city except the name and purpose.
Other guilds are also organised on the local level - the leader of the Mages’ Guild in one city has no authority in any other city. However, they are at the same time striving towards a more global approach, most clearly visible in the fact that membership is generally accepted across large areas, and someone who is a Thieves’ Guild member will be allowed into any Thieves’ Guild hideout while any student of any university will be allow on the campus of any other university and will be considered a student there.