Citadel

The Citadel is believed to be a construct of the extinct Protheans. It is the location of the Citadel Council and the capital of Citadel Space. It is arguably the most important location in the galaxy.

Presidium
The Presidium is the gleaming heart of the Citadel. Located in the 10km wide ring in the centre. It is home to the offices of the Citadel Council in the Citadel Tower, and the office of Earth councilor Donnel Udina. The Presdium is featured in Inquistion and Homeworlds Issue #2. It also contains the Citadel Embassies.

In Inquistion Captain Bailey states that he has never been comfortable on the Presidium, with the 'well to do' and the politicians. He also says it is not natural, and its sterile.

Citadel Embassies
In Homeworlds Issue #1 James Vega is shown in the Embassies amongst hundreds of other refugees, asking if there is any news about his family on Earth after the Reaper invasion.

Mass Effect: Incursion
In Mass Effect: Inquisition Bailey is a C-Sec officer working on the Citadel in 2186. He is asked by Earth Councilor Udina, to investigate corruption with Executor Pallin.

Mass Effect: Homeworlds
In Mass Effect: Homeworlds Tali and Keenah stow away on a Turian cargo vessel on Ilium to the Citadel, after finding a recording on a Geth that they deemed important enough to show the Council. One there they are arrested by C-Sec when they arrive. They are allowed free and they try and see the Council, but are attacked by Jacobus before they can, Keenah gets shot, and Tali is grazed. They flee inadvertantly into an incinerator, and where Keenah dies, Jacobus breaks in and Tali burns him and escapes.