In the universe of Warhammer 40,000
the Inquisition of the Imperium
is tasked with keeping watch over the teeming billions of the galaxy, and ensuring its loyalty to The Emperor
It is split broadly into three main Orders, which is once more the oft-bastardised latin much loved of Games Workshop.
The Ordo Malleus is tasked with seeking out and destroying the daemonic taint of Chaos, and its chamber militant (specialised force) is that of the Grey Knights; a space marine chapter specifically created to combat the ultimate evils of the ruinous powers.
The Ordo Xenos, whose job is to destroy the alien's corrupting influence on mankinds mind, body and soul. Responsible mainly in the fluff (background story of Warhammer 40,000) for running around after heathen artifacts of the Eldar, collecting as much information on the Necrons as is possible, and eradicating Tyranid Genestealer cults. Their forces are the Deathwatch, small groups of specially selected Space Marines from the ordinary chapters spread throughout the galaxy so that they might quickly head to an alien influence and destroy it.
The Ordo Hereticus is meant to keep the minds and souls of the billions of citizens of the Imperium in line, bringing those unfaithful back to the light of The Emperor by any means, and if it means their death into the bargain, so be it. Their chamber militant are the Sisters of Battle, the nuns with guns. Orphaned children who were taken in by the Administratum, and raised to love the Emperor till death, and to serve him totally and him only.
The broadness of the Inquisition is further complicated by the different philosophies of the individual Inquisitors themselves.
Thorian Inquisitors believe that the soul of the Emperor has slid into the Warp, and takes the form of extraordinary men who further the Imperium, and hence believe that Sebastian Thor is one such incarnation of The Emperor. They seek to find one day a vessel worthy of binding the Emperor's soul to the mortal coil permanently, but opponents have raised the valid point that the resulting civil war would rent the Imperium in two.
Monodominants are Inquisitors who put their faith in the works of Inquisitor Goldo, who wrote the treatise "Monodomination: The Right of Man to Rule The Galaxy in The Emperor's Holy Name." As might be expected, it preaches xenophobia to the extremes of even the Warhammer 40,000 universe, and in particular the eradication of all alien races so that the galaxy is ruled over by Man and man alone.
Amalathan Inqusitors are fiercely suspicious of change, and seek to maintain the status quo of the Imperium.They are primarily concerned with seeking out and disposing of anyone who interferes with the wishes of the Imperium, and see the purpose of the Inquisition to maintain the Imperium as the Emperor sees fit; and are deeply mistrustful of the Inquisitors who wish to progress.
Xanthites are Inquisitors who seek to harness the power of Chaos for the good of mankind. They investigate all aspects of the warp and chaos, often investing it into themselves and destroying it only when neccessary. Most Inquisitors of this kind are subject to lynch mobs of others that expose his/her dealings with chaos, pronounce them a heretic, and execute them in time honoured ways such as burning witches or by shooting them in the head.
Recongregators are the opposite of Amalathan Inquisitors,who view the Imperium as no longer serving the purpose for which it was created by the Emperor, and instead works in spite of them. They seek to place influential and progressive men in positions of power and authority in the view that the resulting new blood will infuse the Imperium with a new sense of purpose and efficiency.
Istvaanians are committed to strengthening the Imperium through war, since it is at these times that Mankind is committed and bound together by a common sense of purpose. Their philosophy basically boils down to good things can come of bad events. Didnt the Horus Heresy weed out the marines unloyal to the Emperor? Did not the Age of Apostasy herald the coming of Sebastian Thor and the reformation of the Ecclesiarchy? They argue that it is only at times of such trouble that mankind shows what it is made of and rises to the challenge. This brings them into conflict with other Inquisitors, since as they are investigating a destructive organisation, all too often they are founded and sponsored by an Istvaanian.
Information gathered from the Inquisitor rulebook, copyright 2000 Games Workshop Ltd. The Living Rulebook incarnation of said rulebook can be found for free download at http://www.specialist-games.com/inquisitor/tlr.asp