The Dreaming is the home of dreams and nightmares alike. All stories written and unwritten, all songs sung and unsung. It is to the Dreaming that mortal minds travel when asleep. The ideologues and even Primarchs find their first nascent sentience in the Dreaming, pulled together by flicking sparks of intent married to the heat of the Source.
The Dreaming's relationship with the Fae is very mercurial. The denizens of the Fae Realms sometimes are cooperative and helpful, and at other times have been antagonistic and exploitative. The Dreaming is a realm for mortals and the Fae are not above trespassing the border region between realms to toy with mortal dreamers.
The Dreaming is closely allied with the guardians of Otherworld. It is at the walls of The Dreaming that the gates to Nullspace can be found, and the Unseelie Court sends an endless flow of warriors to man the battlements and repel invaders or sappers.