Board Thread:Online Discussion/@comment-3076045-20131027121334/@comment-3076045-20140318012007

WC-83 wrote: so players can make their own guild or is it limited to guilds such as the Fighter's Guild, Companions, and College of Winterhold? Neither of those are in the game, but Fighters and Mages guilds are. These are the more tradional guilds both in lore (see Guilds Act), and the series itself (theyre present in just about every game except Skyrim. Incidentally, this was designed to signify just how end-of-time the period really is).

And to answer the other part... You can join up to 5 player-made guilds, and all NPC guilds. (Thieves guild and dark brotherhood will be added post-launch)