The Commonwealth

The Commonwealth is what is left of the pre-War American state of Massachusetts in New England. While traditionally called a commonwealth in itself, before the Great War, Massachusetts was also part of the New England Commonwealth of the United States in the alternate history of the Fallout universe. Most of it is a war-ravaged quagmire of violence and despair like much of the rest of the former United States, but it is also where the mysterious Institute is located.

Organizations
The Institute is likely the descendant of the Massachusetts Institute of Technology. Little is known about The Institute other than that the scientists working in the sealed environment possess highly advanced technology and technological skills. The Institute has created true artificial intelligence (AI) and is capable of manufacturing androids, also referred to as "synths" - short for "synthetic human".

Another organization active against the Commonwealth, the Railroad, functions in direct opposition to the Institute. Named in honor of the Underground Railroad, the Railroad's mission is the rescue and salvation of synthetic humanoids.

There is a special branch of the Commonwealth Police called the Synth Retention Bureau. It is tasked with recovering synths that attempt to escape from the Institute.

Appearances
The Commonwealth is only mentioned in Fallout 3 and its add-ons The Pitt, Broken Steel, and Point Lookout.