The Commonwealth

 is an organisation of scientists that operates from their main base called "The Institute," a place to the north of Washington, D.C. Little is known about the Commonwealth other than that they possess highly advanced technology and technological skills. The Commonwealth has created true AI and is capable of creating convincing androids. "The Commonwealth" may very well refer to the Commonwealth of Massachusetts, and "The Institute" would then refer to the Massachusetts Institute of Technology.

Harkness, Dr. Zimmer and Armitage are from the Commonwealth.

Apperances
 is only mentioned in Fallout 3.