Group of four sectors within the Imperium under the general control and direction of an Archduke.
The Domains are listed below in order of creation.
| DOMAIN | SECTORS |
| Domain of Sylea | Core, Fornast, Massila, Delphi |
| Domain of Vland | Corridor, Vland, Gushemege, Dagudashaag |
| Domain of Gateway | Ley, Gateway*, Glimmerdrift Reaches, Crucis Margin* |
| Domain of Ilelish | Ilelish, Zarushagar, Reavers' Deep, Daibei |
| Domain of Antares | Meshan*, Mendan*, Lishun, Antares |
| Domain of Sol | Diaspora, Old Expanses, Solomani Rim, Alpha Crucis |
| Domain of Deneb | Spinward Marches, Deneb, Trojan Reach, Reft |
| * denotes that although, technically, a part of a Domain, these sectors are outside of the Imperium |
This coverage leaves 3 sectors outside of the technical boundaries of the Domains. Empty Quarter is ruled from the Domain of Antares. Hinterworlds are part of the Domain of Sol, and Verge is a part of the Domain of Ilelish. Also for practical reasons, the rimward-trailing portion of Reft sector is controlled by the Domain of Vland.