Citadel Station, or simply Citadel, is a fictional space station orbiting Saturn, within the futuristic cyberpunk universe of the System Shock series. Prior to the incident with SHODAN, the TriOptimum was negotiating the employment of Citadel in mining operations on the Saturn's moons with the United Earth Miner's Conglomerate.

The station is a massive space structure constructed by the TriOptimum Corporation for research and mining purposes. Facilities range from neural surgery to luxurious executive suites, rendering the station more than capable of performing any given task.

According to the schematics in the introduction, the length of Citadel is 427 meters, it weighs in at 2 million metric tons and has a crew of 430, although it looks like 438.
The station is overseen by a complex and highly evolved artificial intelligence, SHODAN.

It comprises of ten levels, each serving a specific purpose. Additionally, along the rim of the executive level, four eco-pods, known as groves, (dubbed Alpha, Beta, Gamma and Delta) are located, accessible via airlocks.
From top to bottom, the levels are Bridge, Security, Engineering, Executive, Flight Deck, Cargo Bays, Maintenance, Research, Medical and the Reactor.

The station is designed to be completely secure; computer nodes on each level ensure the optimal operation of the station's AI, and distributed software guarantees that the AI will not cease to function even if one or several of its nodes is lost in an accident; a camera system monitors every level (feeding directly to SHODAN), ensuring that medical, repair and automated security robots are immediately sent where needed; and finally, every level has reconstruction machinery that can mend even the most terribly mutilated human body.
In case of an irrecoverable emergency, the Flight Deck has several multi-man escape pods. The bridge section of the station is also designed to be separable from the main body and serve as a massive escape capsule; finally, the recreational groves are linked to the station with explosive bolts and can be jettisoned into space from the other side of their airlocks.

Citadel was destroyed by the hacker in order to thwart one of SHODAN's attempts to destroy humanity. The bridge section separated and travelled towards Earth. Fortunately, SHODAN was defeated in cyberspace by the hacker before the bridge section reached Earth.