Looking Glass Studios was the game development company behind the Thief series as well as System Shock.
It was founded in 1990 by Paul Neurath and Ned Lerner in Cambridge, Massachusetts. The company went out of business in 2000 due to a financial crisis with their publisher at the time, Eidos Interactive, as well as very poor sales of their two self-published games. The final game to be completed and released was Thief II: The Metal Age.
Before closing the company graciously released DromEd, its level designer and editor, to the fan community. This lead to a dedicated fanbase creating a number of fixes for their published games and even a few fanmade missions.