A Cardinal World is an Imperial planet ruled directly by the Ecclesiarchy that is completely dedicated to the worship of the God-Emperor according to the tenets of the Imperial Cult, with Imperial sanctuaries, cathedrals and temples potentially covering entire continents. Aside from already also being classified as a Shrine World that is a particularly important centre of the Ecclesiarchy's power and a destination for the countless pilgrims of the Imperial Cult, Cardinal Worlds also serve as a base of operations for many orders of the Adepta Sororitas. One example of an important Cardinal World is Ophelia VII, whose spiritual significance to the Imperial Cult is second only to that of Terra. The Planetary Governor of a Cardinal World is always a Cardinal of the Adeptus Ministorum, who often leads the Ecclesiarchy's hierarchy in an entire sector of Imperial space.
- Dark Heresy: Core Rulebook (RPG), pg. 250
- Warhammer 40,000 Core Rulebook (3rd Edition), pg. 114