The Ordo Hereticus is the largest of the ordos and its Inquisitors watch for enemies among the Imperium’s own population. Members of the Ordo Hereticus are sometimes known as “Witch Hunters” because of the priority they place on apprehending psykers. Mutants, rebels and heretics are also targeted by the Ordo Hereticus. The Ordo has no qualms at all about acting against threats in the other Adepta and many a renegade Ministorum cardinal or corrupt Tech-Priest has met his end at the hands of a Witch Hunter.
The Ordo Hereticus often makes use of Imperial forces, like the Imperial Guard or Adeptus Arbites, to aid in the fulfilment of its duties. However, armed forces led by a Witch Hunter Inquisitor frequently include Sisters of Battle. Centuries ago, following the Age of Apostasy, the newly reformed Adepta Sororitas and the Ordo Hereticus forged an agreement to assist one another in fighting the Emperor’s enemies. This agreement, made at the Convocation of Nephilim, is still shrouded in mystery and it is suggested among some Inquisitors that the Sisters of Battle and the Ordo Hereticus are following some secret plan that only the canonesses of the Sororitas and a few Inquisitor Lords fully understand. Whether this is true or not, a Witch Hunter can expect to find common purpose with the Sisters of Battle, and the two organizations work together extensively.
Inquisitors of the Ordo Hereticus are commonly figures of incredibly strong will. Some are fitted with special psychic hoods designed to nullify hostile witcheries targeting their mind or person. Others prefer to trust in the Emperor, uttering litanies of protection and hate as they move against rogue psykers. As with the other ordos of the Inquisition, the Witch Hunters are happy to use individuals with psychic powers, provided they have been properly sanctioned. Perhaps surprisingly, there are many Inquisitors amongst the Ordo Hereticus who are capable of using psychic disciplines themselves. Woe betide the witch who is hunted by one such individual, for these Inquisitors are notorious in their zeal. Perhaps it is because they are fully aware of the terrible dangers that lurk within the warp, or perhaps it is a result of their training---whatever the case, these psychic Witch Hunters will stop at nothing to destroy the corrupt and tainted.
Some Inquisitors within the Ordo Hereticus specialize in the identification and eradication of mutants. They may have numerous cells of Acolytes at their disposal, which range from hive-toughened flamer squads, trained to purge large infected areas, to precision assassination cells, which remove and replace key political figures that have succumbed to the lure of the Dark gods. In most cases, such Inquisitors will be less concerned with the mutants themselves (as they are a relatively simple matter to deal with) and more with the causes of mutation. An outbreak of mutation may herald a terrible event, point to an upswing in cult activity or simply be the inexplicable whim of the Ruinous Powers. Whatever the cause, the Ordo Hereticus will require an investigation and purge. This can sometimes cause the Ordo to be involved in high-profile events, such as the removal of a head of state, the cleaning up of corrupted pollutants or even outright war.
Occasionally the Ordo will find itself pitted against an individual being or phenomenon which presents a significant threat. This might be as varied as a psyker of unprecedented power, a mutant with terrifying abilities or even a governor unwilling to carry out necessary pogroms. In such cases, the Ordo Hereticus will excommunicate the offending person from the human race and then hunt them down with frightening ruthlessness. The ordos will call upon any allies they feel necessary, from the Sisters of Battle, to members of other Adepta or servants of another ordo. They are willing to do whatever is needed to get at the excommunicated party, even if it should mean sending the Imperial Guard against the Imperium’s own people. Better to end a thousand innocent lives than to suffer the spread of corruption.
Perhaps more so than other arms of the Inquisition, the Ordo Hereticus is concerned with the big picture. Their duty tasks them with tending to a vast flock, and as such, individuals within that mass are seldom of importance. The Imperium is comprised of billions of souls, each of which is a potential psyker, mutant or rebel. The Ordo Hereticus fights on countless fronts, endlessly, with no warning of where fresh heresy may arise. Whilst cells of Acolytes or particular Inquisitors may have the luxury of dealing only with the local situation, the scholars and masters of the Ordos look upon events with a distanced eye, thinking in terms of systems and sectors rather than planets or countries. To some observers, this impersonal attitude is vile, but to members of the Ordo Hereticus it is necessary to protect mankind from itself.