Administratum

The Administratum: more red tape than a planet can hold. We're not joking: there is a planet on the verge of a civil war because it is literally out of space on where to store the files.

The Adeptus Administratum is the name of the pencil pushers of the Imperium of Man. Founded by Malcador the Sigillite back in the day the Emprah was strutting about, the Administratum is the bureaucratic division of the Adeptus Terra. They assess the tithes every world must pay to the Imperium, take census data, and maintain records. Unfortunately, ten thousand years of bureaucracy has created red tape that stretches for light years and inertia that can (and has) cost wars. Imagine the Vogon equivalent of the Department of Motor Vehicles with all the grimdark of Warhammer 40,000 and half of the productivity; then multiplied by the number of planets in the Imperium. The Adepts of a department will keep going about their duties long after their department has become completely useless. That's the Administratum. It's run by the aptly named Master of the Administratum, who is the most powerful of the High Lords of Terra (because he can threaten to get anyone so bogged down in red tape they will never see the end of it in the span of their lives).

The recent of the Imperium routinely despises the Administratum; even the arbites and the Inquisition admits they are highly inefficient. The Astrates and Guard are more straightforward in their thoughts, thinking that not a few wars could be won if they gave each Admin adept a lasgun and sent them to the front lines. However, as much as they are disliked, all other departments need the Administratum, as they won't know where to go to start ordering basic supplies even if they were desperate enough to try. In the far grim future, the ordering form is a dark and mystical document that requires much ritual and mediation before it can be filled in.

Divisions

• Departmento Munitorum: The section of the Administratum charged with running the Imperial Guard, but the Guard is so massive that even they cannot give an exact number on how large it is. The Munitorum decides which planets have met their tithe requirements or not, but on a few occasions rounding errors or misspellings have resulted in worlds being declared traitors or wiped out regiments being sentenced to death posthumously.
• Estate Imperium: Charged with maintaining the records of the Imperium. The Chancellor of the Estate Imperium can occasionally get a spot on the High Lords of Terra. Well, were he not doped-up on anti-depressants to deal his raging OCD, anyway.
• Historical Revision Unit: The propaganda branch of the Imperium, charged with making sure Imperial history makes the Emperor and the Imperium look perfect and eliminating all knowledge of traitors. Because the Imperium wasn't grimdark enough, they cut/paste the Ministry of Truth into one of their foundational institutions. However, they must have done it with Linux, because they didn't manage to get enough of in to really affect the universe. Although... there has been a shit ton of 'revisions' to a wide variety of things to make various institutions look so unrealistically good that it defies sanity, and yet it has become 'fact'... Well played GW... On the other hand. This lack of knowledge of the very existence of traitors could be very useful in...other ways.
• Officio Agricultae: The department charged with overseeing agriculture in the Imperium, serving to determine the tithes of the various agri-worlds that litter the Imperium, and making sure that that there is enough food to feed the people of the Imperium. Food will still not be distributed equally, which goes to show that even after 30,000 years some things don't change.
• Officio Medicae: The department charged with medical affairs of the Imperium. Unless you're a noble, Guardsman, or Inquisitor, you won't be getting access to any meaningful medical assistance without visiting a dread-inducing back alley doc, who is always located in the underhive, smells of Obscura, and whose services cost an arm and a leg. Sometimes literally.