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Warhammer 40k Inquisition guide

The Inquisition is a secret organization that answers only to the Emperor, its agents battling unspeakable threats to the Imperium of Man.

Warhammer 40k Inquisition - Inquisitor Gregor Eisenhorn, a dour man wearing ornate robes and clothing, equipped with an ornate gold-chased bolt pistol, with a skull-tipped staff attached to his back

The Warhammer 40k Inquisition is a powerful and occult institution, a vast network of powerful Inquisitors and their agents that collectively find, investigate, and destroy threats to the Imperium that normal humans are not permitted even to know exist. This guide introduces the different Ordos of the Inquisition, how to field an Inquisition army in Warhammer 40k, the legendary inquisitor Gregor Eisenhorn, and more.

If you’re keen on Warhammer 40k lore, we have separate guides to each of the Warhammer 40k factions, broken down into guides for the Imperium of Man, Xenos races, and 40k Chaos powers.

Here’s what you need to know about the Warhammer 40k Inquisition:

Warhammer 40k Inquisition - Inquisitorial acolytes attempt to break up a Chaos ritual

What is the Warhammer 40k Inquisition?

The 40k Inquisition is a secretive and powerful organization tasked with uncovering and destroying the threats of aliens, daemons, and heretics, wherever they may lurk within the Imperium. Inquisitors have near unlimited authority to condemn the guilty and pursue their investigations wherever they may lead. They hold the authority to condemn whole worlds to the fiery death of Exterminatus.

The Inquisition was founded shortly after the Horus Heresy, its remit to battle the forces of Chaos and control knowledge of the atrocities that had been unleashed during that apocalyptic war. Many of its founding members were former agents of Malcador the Sigillite – closest friend to the Emperor of Mankind, and regent in his absence – while others played important roles in the Siege of Terra. Since then it has grown and changed, developing new organs in response to new threats.

Warhammer 40k Inquisition - Inquisitor Coteaz, wearing golden armor, holding a hammer and a two-headed eagle

The Inquisition acts in secret, gradually unpicking conspiracies and hidden treason before bringing them into the light to be destroyed. The Inquisition often acts as a censor, ensuring that potentially dangerous information is sequestered away from the public. Yet it is to this same forbidden lore that Inquisitors must turn when seeking the tools to destroy their most deadly foes.

Each Inquisitor has immense power, answering only to the Emperor of Mankind (at least in theory), and able to call upon any resources the Imperium has to offer. When they do need to act in the open, they are able to field substantial armies both of their personal staff, and military personnel requisitioned from the Astra Militarum, Space Marines, or the Militant Chambers pledged to their Ordos.

Warhammer 40k Inquisition - black and white illustration of a radical Inquisitor, driven mad with chaos power

Radical and Puritan Inquisitors

The Inquisition has never been united behind a singular purpose. Each Inquisitor has their own interpretation of how best to defend the Imperium, and political and philosophical disputes are commonplace. The most broad is the split between Puritan and Radical factions, a spectrum of tendencies that describes how willing an Inquisitor is to use proscribed technologies or sorceries to battle the forces arrayed against the Imperium.

The most extreme Puritans ascribe to the Monodominant tendency, which holds that all forms of psychic power, and all non-human sentient species, must be eradicated from the galaxy – an untenable position for an Imperium that relies so heavily on 40k psykers for travel and communication.

The most Radical position is held by the Horusians, who believe that it is possible to create an avatar of Chaos, similar to Horus Lupercal, that could be controlled for the betterment of mankind.

Warhammer 40k Inquisition - three inquisitorial acolytes, damaged humans in dark robes equipped with unique weaponry

The Major Ordos of the Inquisition

The Ordos of the Inquisition are relatively self-contained institutions, each with a specific remit within its overarching mission of defending the Imperium from corrupting influences. While there are countless lesser Inquisition Ordos, each concerned with a specific region of space, particular threat, or philosophical tendency, most Inquisitors belong to one of the three Major Ordos.

Warhammer 40k Inquisition - a red-robed Inquisitor of the Ordo Malleus with a giant blade stabbing a cursed book

Ordo Malleus

The Ordo Malleus is the oldest branch of the Inquisition, and the one that cleaves most closely to its original mission. The Ordo Malleus is concerned with the threat of Chaos in its pure form, be that cults, Chaos Space Marines, fallen Houses of Chaos Knight, or incursions of Chaos Daemons.

The Chamber Militant of the Ordo Malleus is the Grey Knights, a rare order of psychic Space Marines equipped with the weapons and spiritual training necessary to battle sanity-defying daemonic hosts.

Warhammer 40k Inquisition - an Inquisitor of the Ordo Xenos wearing power armor and equipped with alien weapons

Ordo Xenos

The Ordo Xenos was founded in M32 during the catastrophic Ork Waaagh! known as the War of the Beast. In the face of this existential threat the Inquisition was divided between those who wanted to act against the Ork menace, and those who saw this as a dereliction of the institution’s original purpose. The internal schism was resolved by the creation of the Ordo Xenos, which concerns itself with Xenos threat to the Imperium.

The Chamber Militant of the Ordo Xenos is the Deathwatch. This specialist Space Marine formation consists of Battle Brothers drawn from every Space Marine chapter. This cross-chapter force was also founded during the War of the Beast, initially from Imperial Fists successor chapters rallied to repel the forces of the Orks. Imperial politics holds a well-founded taboo against Space Marine commanders controlling more than 1,000 marines, so the Deathwatch was placed under the command of the Ordo Xenos.

Warhammer 40k Inquisition - Inquisitor Karamazov of the Ordo Hereticus, an aged figure on a walking throne, with heretics burning in a pyre

Ordo Hereticus

Founded in M36, the Ordo Hereticus looks for threats within the body of the Imperium: mutants, unsanctioned psykers, apostate priests, seditious Imperial governers, heretical preachers, and more.

Their order was formalised in response to the Age of Apostasy, a period of dire civil strife within the Imperium. First was the Reign of Blood, when the Master of the Administratum Goge Vandire claimed the seat of the High Ecclesiarch and through it tyrannical rule over the entire Imperium: and then the plague of unbelief, when Cardinal Bucharis created a secessionist empire around his Shrine World of Gathalmor.

The chamber militant of the Ordo Malleus is the Adepta Sororitas. The Sisters of Battle were also inducted into the Imperial fold during the Reign of Blood, initially serving as Vandire’s elite bodyguard under the misapprehension that he was a living saint, before siding against him when the truth was revealed to their leader.

Warhammer 40k Inquisition - an Inquisitor leading a mixed force of Adeptus Custodes and Adeptus Mechanicus forces

How do you field a 40k Inquisition army?

It’s possible to field a Warhammer 40k Inquisition army in 10th edition using rules from the Agents of the Imperium Index. This contains rules for Inquisitors, Inquisitoial Henchmen, and several Epic Hero Inquisitors.

The “Assigned Agents” rule allows you to take a number of Imperial Agents units in another Imperium-aligned Warhammer 40k faction. This means Space Marines (including all chapter variants), Deathwatch, Imperial Knights, Sisters of Battle, Grey Knights, Astra Militarum, Adeptus Mechanicus, and Adeptus Custodes, can all be joined by Imperial Agents.

Battle Size Retinue Units Character Units
Incursion 1 1
Strike Force 2 2
Onslaught 3 3

Warhammer 40k Inquisition - closeup on an Inquisitor wearing power armor, illuminated by lightning,

Inquisitors can be added as leaders to any Imperium Battleline unit. Their ‘Authority of the Inquisition’ ability permits them to ride in any transport that their Bodyguard unit can be embark within. As Characters they can be assigned to be your army’s Warlord, though they lack any key words that would allow them to take Enhancements.

You can represent an Inquisitorial army for each of the major Ordos quite easily by adding an Inquisitor to the respective Chamber Militant: Sisters of Battle for the Ordo Hereticus, Grey Knights for the Ordo Malleus, or Deathwatch for the Ordo Xenos.

And any Inquisitor might requisition Astra Militarum forces, call in oaths of support from a Space Marine Chapter, Knight house, or Forge World, or petition for aid from the Adeptus Custodes.

Warhammer 40k Inquisition - Inquisitor Gregor Eisenhorn, a dour man wearing ornate robes and clothing, equipped with an ornate gold-chased bolt pistol, with a skull-tipped staff attached to his back

Who is the 40k Inquisitor Gregor Eisenhorn?

Gregor Eisenhorn is the most famous 40k Inquisitor, thanks to his starring role in an excellent Warhammer 40k book series by Dan Abnett. He is still an active character in the Warhammer 40k lore, appearing in the still-unfinished Bequin series.

Eisenhorn is a member of the Ordo Xenos within the Scarus sector of the Segmentum Obscurus. The three Eisenhorn novels trace his journey from a (fairly) puritan junior inquisitor to a radical and ultimately exiled veteran. The books have major time skips, reflecting the extended lifespan of an Imperial Inquisitor and the incredibly slow pace of change in the Imperium.

Several key characters originate in the Eisenhorn novels. By the second book Eisenhorn has taken on an apprentice, the Interrogator Gideon Ravenor, who gets his own spin-off series. Eisenhorn’s close confidant, the psychic null Alizabeth Bequin, is sent into a coma in the third Eisenhorn novel – what seems to be her reincarnation appears in the as-yet unfinished Bequin series. The daemonhost Cherubael is also an incredibly important part of Eisenhorn’s journey.

Dan Abnett wrote the original Eisenhorn very rapidly, after learning about the wargame Inquisitor and discovering that no-one was writing a tie-in novel for it. Eisenhorn is a mixture of cosmic horror, James Bond, and a modicum of John le Carré. However, concepts that Abnett introduced in it (and the Ravenor spin-off) have made their way into the deep lore of 40k, including the recently-concluded Horus Heresy series, and the cliff-hanger at the end of Bequin: Penitent is absolutely dripping with lore implications.

Warhammer 40k Inquisition novels - three pictures of the Inquisitor Gregor Eisenhorn

The best Eisenhorn reading order:

Wargamer recommends following the Eisenhorn publication order when reading the series, not the chronological order. The short story collection and novella ‘The Magos’ is set chronologically before ‘Bequin: Pariah’, but it was written afterwards, and it shows.

  1. Eisenhorn: Xenos
  2. Eisenhorn: Malleus
  3. Eisenhorn: Hereticus
  4. Optional – Ravenor
  5. Optional – Ravenor: Returned
  6. Optional – Ravenor: Rogue
  7. Bequin: Pariah
  8. Eisenhorn: The Magos
  9. Bequin: Penitent

Eisenhorn TV series

In July 2019, Games Workshop announced that an Eisenhorn TV series was in development. Big Light Productions was named as heading up development, with Frank Spotnitz (a former X-Files writer and the show runner for the Amazon Prime adaptation of ‘Man in the High Castle’) in charge of the project.

Since Games Workshop announced its partnership with Amazon Studios for the Warhammer 40k Henry Cavill film and TV series project in 2022, it’s not clear  whether development on Big Light Production’s Eisenhorn series is continuing. It may have been abandoned, or it may have been incorporated into the new project.

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The Eisenhorn video game

There is an Eisenhorn video game, Eisenhorn Xenos. It reviewed very badly, and we’ll confess to not having played it yet. You can watch YouTuber William SRD’s video review, above.

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What is Warhammer 40k Inquisitor Martyr?

Inquisitor Martyr is a Warhammer 40k game on PC, Xbox One, Xbox series S|X, Playstation 4, and Playstation 5. It’s an action RPG in which players take on the role of an Inquisitor tasked with uncovering mysteries and fighting corruption in the Calligari sector. It can be played solo or in co-op mode.

While it’s not in contention for the best action RPG of all time, it’s definitely the best Warhammer 40k ARPG. It’s action focused. Players explore gothic environments and fight hordes of cultists, mutants, daemons, Chaos Space Marines, and other nasties using a variety of ranged and melee abilities.

Skills are linked to your choice of weapons, and to your character class and upgrades. The game includes a cover system and destructible terrain, and the sense of carnage from unloading a chugging heavy bolter or going absolutely ham with an eviscerator chainsword is excellent.

On launch, Martyr was only available to play in an online mode featuring an online leaderboard, seasonal content, and multiplayer. A new offline mode launches in May 23 2024.

For a deep dive into another shadowy agency working behind a veil of secrecy to protect the Imperium, check out our guide to the Warhammer 40k Assassins.