Dark•Matter is a science fiction/conspiracy theory campaign setting set in the modern day. It was originally published in December 1999 by Wizards of the Coast as the second campaign setting for the Alternity science fiction role-playing game. It was written by Wolfgang Baur and Monte Cook. It was later converted to d20 Modern rules as a stand-alone book in 2006.

Alternity is a science fiction role-playing game (RPG) published by TSR in 1998. Following the acquisition of TSR by Wizards of the Coast, the game was discontinued in 2000 as part of a broader rationalisation of TSR's business holdings, but it retains a small and devoted fanbase. Parts of Alternity as well as TSR's classic Star Frontiers game have been incorporated into the d20 Modern game, especially the d20 Future setting. The first campaign setting for the Alternity game, the Star*Drive setting, was introduced in 1998.