Organized crime

Thieves Guilds usually aren't much more than handy sources of protection, places for trading stolen goods or gathering information with little sense of organization beyond a ragtag group of ruffians who share some resources such as hideouts, so, they shouldn't usually be considered for this. Small gangs of highwaymen shouldn't be considered it either.

Popular examples: (real world)
* Italian Mafia (actually Sicilian, a.k.a. Cosa Nostra)
* Chinese Triads
* Japanese Yakuza

Popular examples: (fictional)
* Thieves' Guild
* Assassins' Guild

Related:
* Gangsters