I'm planning to base a DH campaign on a single world, probably an agri world. I want this world to be different to what passes for a typical world, while keeping it as a world that is regarded as loyal by the rest of the Imperium (or at least the people who know much about it).

So what are the things this world must have to be regarded as a loyal and faithful world ?

I've started running into a lot of the same kinds of questions recently while developing an incredibly "radical" storyline starting in Dark Heresy . That said, I think the answer to your question is very easy: any backwater planet can essentially be guaranteed security so long as it's Administratum-dictated tithe is transferred to Scintilla (or, for an agriculture world, the shipments end up where they are supposed to without problems). I don't see any reason why there would be any sort of Adepta presence on an "out of the way" agriculture world, except perhaps Administratum and Ecclesiarchial personnel.

I know that isn't too much of an answer, but - and again, this is just in my own little 40K galaxy - such concepts as being held in good favor and considered loyal seem very limited for singularly productive worlds (agriculture, forge, etc.). Be quiet (or don't draw attention, since it should be easy), fulfill tithes, and remember that no one cares where the food in the supermarket comes from - they just expect it to be there.

There actually is an answer to this question somewhere in the core rulebook. I think it boils down to:

- The planet must render its tithe to the Administratum without fail.

- The planet must attempt to detect all the psykers in its population and deliver them unto to the Black Ships.

- The planet must only allow one religion- faith in the God-Emperor in an at least nominally sanctioned form.

- Generally, contact with xenos is not allowed, but there are some exceptions made for backwater worlds.

Worhsip the Emperor and no others, in a manner not considered heresy by the ecclesiarchy.

Give the pyskers of your world to the black ships.

Pay the Emperor's Tithe.

See to your defense, and provide for the defense of the Imperium as needed.

Do not trade with or porvide succor to the enemies of mankind.

Thats it. Everything else is negotiable. Now...how much security and scrutiny a world recieves is directly relatice to its percieved value to the Imperium and its ability meet the big ones. A true backwater might have just enough administratum to make sure the Tithe goes smoothgly, just enouh Ecclesiarchy to make sure its not a heresy in the brewing, a handful of astropaths, and thats about it. The planet might not see anything other than the odd trader and tax collector for decades or more. Its quite possible that the entire planet could be conquered and no one would notice until the tithe collection failed.

Hodgepodge said:

You could probably add "Purge the Unclean" in regards to mutants to that list, though to some extent there is leniency to have them isolated from the mainstream community locked up somewhere horrible.

Aside from that, the planet can mostly do what it wants in regards to laws, culture and preferences

In addition to the above, there will always be a single individual with the title "Planetary Governor" that is held responsible for fullfilling this to the Imperium. In the standard case, the Imperium doesn't even care how this person is decided upon. So it's perfectly fine to have any kind of political system, as long as the above criteria is fullfilled and one person is appointed Governor. The Imperium also claims the right to appoint a Governor or change the method of appointing her/him if it is deemed neccessary to keep the planet in line. Feodalism with hereditary lordships seems to be the standard political "solution".

The Adeptus Mechanicus have a semi independent Imperium with the Imperium. Most Forgeworlds are directly governed by them for example. I must confess that I do not know much about how they rule their worlds or what parts of the above requirements they actually do follow. Maybe someone can enlighten me?

Besides, there is not even need for any tithe as long as the planet is still considere a colony. There seems to be some kind of "close season" till the colony reaches "majority" is reached.

Yeah, there seems to be a legal grace period. If I remember correctly, Quaddis is only "sort of" part of the Imperium and pays no tithe because the Rouge Trader who discovered it (one of the Haarlocks) tied its administratum status up in clever legal knots- which the many nobles, Inquisitors, and Adepta who now have estates there have no desire to see cut through.