Psykers are sentients that can call upon the powers of the Immaterium to manipulate, or even break them completely, the laws of physics. They can read minds, communicate across the stellar voids, control perceptions and emotions, throw objects around, manipulate fire, call forth daemonic entities, see into the future, move by teleportation – basically anything is possible; this is, for all intents and purposes, magic.

Grading Psychic Power: Legend holds that the Emperor himself designed the terms by which the Imperium grades potential psychic strength. The following gradations are designated in one of the truly ancient languages of Holy Terra in order of ascending power levels. The designations are not exact; there is some variation of power within each grade. Neither are the grades meant to be an exacting mark of ability, but rather, of raw power potential. A well-trained psyker of a lesser grade has a decent chance of beating a stronger, but untrained psyker. The trained psyker is also far less likely to become warp tainted or driven insane. The grades also does not say what type of powers the psyker can manifest; many psykers have a talent only for certain manifestations only or have lesser power/ability when it comes to applications of psychic power outside their primary talent.

Minor Grades: Note that there are many lesser grades of psychic ability than Zeta, but they are all but undetectable without the most sophisticated of equipment. Below the Theta Grade psykers do not manifest any powers, not even subconscious minor ones. In rare cases a sub-Theta might grow in power potential, but this is exceedingly rare. The Imperium cannot identify sub-Theta psykers at all; there is no known equipment that is able to measure such weak psychic flows, nor will a sub-Theta be identifiable to another psyker.

Theta Grade – Theta Grade psykers are virtually undetectable, even if placed under the scrutiny of an Inquisitor using sophisticated psychic detection gear. They are not likely to ever manifest any powers, except under the most unusual of circumstances. Fortunately they are also highly unlikely to attract the attention of anything from the other side, and the complete lack of manifestations also keeps the safe from general warp corruption. It is interesting to note that the average Ork warrior is a latent Theta grade psyker.

Game mechanics: Theta Grade psykers have no psy-rating or psychic powers. They are also very unlikely to suffer from uncontrolled manifestation, corruption, or possession. It is only possible to detect a Theta Grade psyker using specialize equipment, and even then the detection test is Very Difficult.

Eta Grade – Eta Grade psykers have some psychic potential, but usually only on at a subconscious level. Eta Grade psykers are very difficult to detect by the means available to the Imperium; either a full psychic check using specialized equipment or an experienced Telepath actively searching, is required to detect a non-manifesting Eta Grade psyker. The average member of the Eldar xenos species is an Eta Grade psyker.

Game mechanics: Eta Grade psykers have no psy-rating or psychic powers. They may become nexuses from uncontrolled manifestations and are thus in danger (however slim) of corruption and possession (but only the weakest of daemons would want to possess such a weak soul).Detecting a latent Eta Grade requires a test using appropriate equipment or a skilled Telepath actively scanning; the test is Challenging.

Intermediate Grades: Zeta through Gamma grades are the most common in the Imperium, and the ones most likely to be identified and handed over to the Black Ships. Psykers of below Zeta grade are hard to detect and so often slip through the cracks in the system. Psykers of Beta and above as so strong that they almost invariably require special handling, destroy themselves or go rogue. Zeta to Gamma grades are also have enough strength to be useful if trained, but are not so dangerous that they require special control measures – thus these power grades are the ones most commonly found a trained and sanctioned psykers.

Zeta Grade – Zeta Grade psykers are the most common psykers in the Imperium with a readily noticeable level of ability. Zeta Grade psykers tend to have a few minor psychic powers at most, which they may or may not be able to employ in a conscious fashion. Zeta Grade psykers that go untrained are usually not a major problem to the Imperium; they are generally too weak to attract the attention of major Warp entities, and if they do their inherent weakness will limit to power of the possessor. frequently a beacon to daemons. Untrained Zetas are more of a danger to themselves and the immediate surroundings, as years of exposure to Warp energies are likely to eventually drive them insane or corrupt them in both body and soul.

With rigorous training, a Zeta Grade psyker may aspire to being an Epsilon, but only a few have the will to endure the trials required without loosing their sanity and few Imperial authorities would waste their time attempting to salvage them. Most Zetas end up as offerings to the emperor. A considerable number of mutants have Zeta Grade psychic ability; if taken by the Arbites of Inquisition they will usually be executed on the spot since they are too tainted to be offered to the Emperor.

Game mechanics: Zeta Grade psykers have a psy-rating of 1 or 2, and have at least 1 minor psychic power. Many will never consciously use their power(s), but only manifest under duress or certain conditions. Someone with stronger latent power (psy-rating 2), but no psychic powers could be classed as Zeta+. The same goes for a experienced and strong-willed Zeta (psy-rating 1, but several minor powers or even access to a psychic discipline). Identifying a Zeta grade psyker is an Ordinary test.

Epsilon Grade – Epsilon Grade psykers are less common that Zeta grades, but still common enough. Epsilon Grade psykers are the first with enough power to allow for a more structured use of their talent. Given some experience these psykers can consistently invoke several minor powers and have begun to grasp the fundamentals of at least one psychic disciplines. Epsilons have a greater presence in the Immaterium and untrained specimens will sooner or later attract unwanted attention from warp entities, or just succumb to general mental and physical corruption

A large number of low-profile rogue psykers – known as Wyrds, Warlocks, or Witches – are Epsilon Grade. If possessed they can become a real hazard for local agencies. Sufficient time, training and will can allow an upper-range Epsilon to evolve into a Delta. Epsilon Grade psykers are much sought after by the Arbites and the Inquisition since they make up the bulk of psykers that are inducted into the Adeptus Astronomicon. Those that do not make the Astronomicon are offered to sustain the Emperor, save for a few lucky ones who might end up as sanctioned psykers or commercial-grade astropaths.

Game mechanics: Epsilon Grade psykers usually have a psy-rating of 2 or 3, and have at least one discipline talent and a minimum of one power from that discipline. They will also have a number of minor psychic powers. Old and experienced Epsilons can have many more powers and great skill with those, but they rarely exhibit any great range of powers.

Delta Grade – Delta Grade psykers make up the bulk of Astropaths and sanctioned Imperial psykers. Delta Grade psykers frequently focus a single psychic discipline, although more experienced ones are usually capable of utilizing portions of a second or third. Deltas have a major psychic presence and can become conduits for powerful warp-entities unless they receive the proper training and utilize the necessary wards.

Well-trained Delta Grade psykers are very dangerous individuals, capable of utilizing their abilities to the fullest. Experience and discipline in equal measures may well see a Delta eventually achieving Gamma Grade, if they do not burn out before then.

Game mechanics: Epsilon Grade psykers have a psy-rating of 4 or 5, have a sizable number of minor powers, have several powers from one discipline, and at least one power from a second psychic discipline. A psyker with a psy-rating of 5, high Willpower, many psychic powers, and several appropriate psychic feats would qualify as a Gamma Grade instead.

Gamma Grade – Gamma Grade psykers represents the best of what is commonly available for service to the Imperium. Astropaths of this power, for example, are usually attached to the staffs of important individuals or offices – a Sector capital, and important Inquisitor, a fleet flagship, and so on. Gammas frequently continue to focus on one discipline, but many have talents that branch into one or more other disciplines as well (Astropaths of this level tend to be very potent diviners in addition to being astro-telepaths).

Game mechanics: Epsilon Grade psykers have a psy-rating of 5 at the very least, though 6 is more the norm, have mastered one or two psychic disciplines, and/or have psychic powers in additional disciplines. Experienced psykers of this power invariably have incredible willpower and focus; or if they do not they are warp-corrupted and terminally insane.

High Grades: Beta and above grades are very rare and very potent. They have abilities that allow them to do things lesser psykers cannot. Because of their power Betas and above a very carefully monitored by the Imperium for traces of taint or deviancy. An Beta driven insane by his manifestations could do tremendous damage before being stopped, and the though of a warp-corrupted alpha running lose is utterly terrifying. Betas and stronger psykers also make excellent hosts for even the strongest of warp entities; imagine the horror of an Alpha Plus psyker actually becoming possessed by a Greater Daemon.

Beta Grade – Beta Grade psykers are frequently born, not made, as the raw power that typically indicates this level of ability is almost impossible to achieve with training alone. Many Betas therefore start with only a single Psychic Discipline, though they can usually invoke their various powers with near ludicrous ease and control. The rare Beta Grade psykers who have reached this level through training and discipline are frighteningly powerful individuals who invariably have a wide variety of Psychic Disciplines and individual abilities to draw upon. They usually have a century or more of experience in applying said abilities in a myriad of ways making them phenomenally dangerous combatants. A number of the more powerful members of the Inquisition as well as the bulk of the Librarians of the Adeptus Astartes are Beta Grade psykers.

Game mechanics: A very experienced and potent (psy-rating 6) Gamma may be deemed a low level Beta. Mid and high power Betas have ability potentials not yet covered by Dark Heresy game mechanics (i..e they have psy-rating if 7+, WP scores approaching 100, and most likely talents not yet published)..

Alpha Grade – Alpha Grade psyker are rarely made, but are born, since this level of ability cannot usually be reached through training. Even the strongest Imperial psykers seldom reach this pinnacle of ability; only centuries of careful discipline and rigid self control can ever allow a human (or once-human) mind to successfully achieve Alpha Grade without insanity, warp corruption, or possession. Almost all sanctioned Alpha Grade psykers on record have been either a Master Librarian of the Adeptus Astartes or an ancient Inquisitor Lord.

Game mechanics: Beyond the current scope of Dark Heresy game mechanics. An Alpha Grade would have a psy-rating approaching 10.

Alpha-Plus Grade –Alpha-Plus Grade psykers are those whose powers are so far beyond the norm as to be nearly immeasurable by Imperial science. Their powers are nearly unimaginable in scope, Telepaths capable of mentally dominating the population of any entire Hive hab-block, Telekines strong enough to topple a Battle Titan with a thought, Pyrokines that turn even Astartes in Tactical Dreadnaught Armor into slag, that sort of thing..Alpha-Plus Grade psykers are almost invariably warp corrupted and insane. The Imperium’s policy on all Alpha-Plus Grade psykers is typically immediate termination, though this is easier to state then to achieve.

Game mechanics: Beyond the current scope of Dark Heresy game mechanics; PCs are not intended to reach this level of power. If Alpha-Plus psykers appear in the game they are there as plot devices or major NPCs.

Double Alpha Grade – Double Alpha Grade psykers have powers that are nearly unimaginable in scope. There have been instances where Telepaths have taken control of the population of and entire planet, Telekines strong enough to pull a battleship out of orbit causing it to crash, Cryonkines that have plunged worlds into vicious ice-ages by their mere presence, and other such horrors. The Imperium at large isn't even aware that such psykers can exits; but the Inquisition and the Astartes will know that immediate termination is the only viable option The Emperor was most likely a Double Alpha during his lifetime.

Game mechanics: Beyond the current scope of Dark Heresy game mechanics; PCs are not intended to reach this level of power. If Alpha-Plus psykers appear in the game they are there as plot devices or major NPCs.

Triple Alpha Grade – Triple Alpha Grade psykers are beings of god-like power. There is only one psyker on record who merited this rating, the xenos psyker code-named 'Cacodominus'. He was able to mentally dominate no less than 1.300 star systems before slain by the Black Templars in 401.M34. A telekine of comparable power should theoretically be able to rearrange planetary orbits, a Pyrokine could cause a star to go nova, etc.

Game mechanics: Beyond the current scope of Dark Heresy game mechanics; PCs are not intended to reach this level of power. If Alpha-Plus psykers appear in the game they are there as plot devices or major NPCs.

Latent Psykers: Not all psykers are born with their power level fixed at birth. Almost all psykers are born with their talent (Imperial technology has had little success in making artificial psykers, at least ones that remain sane and whole) and see it bloom as they reach adolescence (although there are those that are active even as infants or small children). For some, however, their latent power never manifests, or manifest at a much lower level than what is their true potential. Such psykers can often awaken their hidden powers with training and instruction, or if they are caught up in monumental and/or threatening situations.

Game mechanics: Dark Hersey characters have the opportunity to advance in power by increasing their psy-rating and gaining various skills, talents and advances that make them more potent as psykers. So you can have PCs that are psykers, but have no real psy-rating nor any powers, but who might with training gain both a psy-rating (though probably not a very high one) and powers later on.

NPC are usually more limited; an would-be astropath gathered by the Black Ships usually has a high psy-rating, but very little else. Once he's been soul-bonded and trained, his psy-rating and other stats will generally remain relatively unchanged throughout his career, unless he's got some special talent or motivation.

Trained and untrained Psykers: Untrained psykers are those who use their powers (consciously or unconsciously) without having received training and thus are unsanctioned. Such psykers are a great risk to themselves and their surroundings. The human mind is not really capable of handing the energies of the warp. Untrained psykers almost always end up at least slightly demented, and many are driven completely insane. Such psykers can of course be quite dangerous. Worse still are those who become corrupted by the warp energies they employ; they can become physically mutated or have their minds so twisted that words like 'insane' and 'mad' cannot begin to describe their condition. Absolutely worst are those that become possessed by an alien intelligence from the Immaterium; a warp-entity. No longer even remotely human, these psykers become hosts to some of humanity's most dangerous and cunning foes.

Training helps a lot, but limiting exposure to the warp and teaching various techniques to ward out unwanted attention. Insanity can be kept at bay (although many experienced psykers tend to be a bit odd or eccentric), warp corruption kept to a minimum, and the danger of possession reduced to near nothing. Most importantly these psykers will know when they are in danger – and can take steps if they are about to succumb (many sanctioned psykers carry a terminal toxin for use in emergency).

Non-psykers: Although there is a certain school of academia that holds that all humans are psykers, however weak, mainstream Imperial science considers anyone below the Theta Grade to be non-psychic. Their potential, if any, cannot be measured and even if they should against all odds be able to manifest, the actual manifestation would be so weak as to be undetectable in itself.

Untouchables: There is a very rare (less than 1 in one billion) human mutation that is effectively anti-psionic. There is some controversy as to whether these untouchable are actually themselves psykers or if they are just non-psychic mutants (the difference is academic at best). Untouchables come in a variety of power levels; some are barely capable of warding themselves against direct manipulation, while a few rare ones can completely nullify psychic powers within a large area.

Psychic technology: The Imperium has access to a variety of technologies that interact with psykers and psychic powers. The following are some of the devices available; psychic detection gear, psychic drugs (to enhance or negate power), force weapons, anti-psionic fields and psychich dampeners, artificial psi-implanted personalities, psy-out weaponry that are extremely lethal to any psychically active entity, the list goes on.