The Dark Eldar race is physically identical to that of other strains of Eldar. Compared to a human, an Eldar is typically taller, thinner of body and limb, more agile and dexterous, and possessed of a greater capacity for rapid thought and mental acuity. There are no significant structural differences between Eldar and humans, and indeed some Eldar are able to pass for humans at first glance. Like all Eldar, the Dark Eldar age at a much slower rate than humans, having a natural lifespan of certainly more than two centuries, and perhaps even longer.

Because of the barbarous nature of their society, the Dark Eldar who become Warriors are markedly quicker and more skilled in armed and unarmed combat that is typical of the Eldar race as a whole. Those Dark Eldar who face the armies of the Imperium are naturally adept at warfare to a degree that requires specialist training of their Craftworld cousins.

The home of the Dark Eldar is a realm known to them as Commorragh (ancient/old Eldar: 'fortress'). The nature of Commorragh is a matter of much debate among those few humans who know of its existence. Some theorise that it is an area of the Eldar webway that has been expanded to contain habitable space; others believe it is something else entirely, merely accessed by use of the webway.

Much of what is known of Commorragh comes from the mouths of poor, broken souls who escaped captivity there. Inquisitors standing at the deathbeds of such people record tales of a vast city, of towering spires beneath a blood-red twilight sky. It is said that the Kabals that control this realm have their homes in massive strongholds where literally thousands of their kind live as slaves and Warriors, while in the streets roving bands of killers prey on any unfortunate enough to cross their paths. Few escape Commorragh with any measure of sanity left to them, and many tales are so wild that it is impossible to give them any credit.

It is not known when the Imperium first encountered the Dark Eldar. By the time the Inquisition confirmed the existence of the race as a separate entity, Imperial endeavours had for millennia been plagued by raiders thought to be piratical offshoots of the Craftworld Eldar already known. As it is known that nomadic bands of Eldar do indeed exist, either as pirates or mercenaries, to separate these encounters from those with true Dark Eldar is a task for which the necessary facts are long-since lost.

Dark Eldar are a warrior race honed to perfection, so far as can be possible for an alien. Their Warriors are expert in the use of the weaponry available to them, and the experience of living in their shadowy home realm makes them masters of hand-to-hand combat. The only aspect of warfare they disregard is psychic power; rumours of Dark Eldar with battlefield psychic abilities are rare, and none have been verified by reliable sources.

The principal weapon of the Dark Eldar is the splinter rifle, a weapon not dissimilar to Craftworld shuriken catapults in that it uses magno-electric force to propel its projectiles. The nature of the projectile, a specially shaped fragment of crystal, allows it greater range than the discs of shuriken weapons, at the cost of impact power. Splinter pistols are carried as side arms by assault troops and worn almost by default by the leaders of raiding parties. Larger versions of the rifles, splinter cannon, possess a highly advanced stabilising mechanism that allows them to lay down a horrendous blanket of fire without impeding the mobility of the firer.

Notable among the Dark Eldar's more advanced weaponry are those devices which use what the Adeptus Mechanicus refers to as 'dark matter'. Commonly found in lascannon-like heavy weapons, but also reported in short-ranged rifle weapons, a dark matter impact is extremely powerful, and almost supernaturally destructive to heavily armoured targets. Many reliable sighting confirm that a single shot from such weapons can bring down such behemoths as Leman Russ battle tanks and even mighty Land Raiders.

The variety of weapons used by Dark Eldar in close combat is almost endless, reflecting their love for this form of battle. All Dark Eldar Warriors, from the most menial trooper to the highest Lord, carry lightweight knives fashioned with monomolecular edges, often tainted with a variety of poisons and toxins. Reports also exist of flamethrower-style weapons that cover their targets with acidic compounds, and launchers that fire what may be a variety of hallucinogen grenade, creating intense terror in its target.

Dark Eldar technology is advanced and ancient, and remains to this day indecipherable to the Adeptus Mechanicus and the Inquisition. It is known, from second-hand reports, that much of their weaponry and vehicles are manufactured by slave labour deep within the strongholds of Commorragh, but the processes and materials used remain a mystery. Their technology encompasses energy weapons, anti-grav propulsion, warp-distortion similar to that of the Eldar webway, and electro-field weapons similar to that used in Imperial power swords.

Dark Eldar technology lacks the Craftworld Eldar feature of direct mental control, and almost all weapons and equipment recovered by the Inquisition possess physical controls. Whether the Dark Eldar lack the ability to manufacture more advanced controls, or whether they simply choose not to, is unknown. Scattered reports of Dark Eldar vehicles and weapons without obvious physical controls exist, but such technology has not yet been recovered. It is worth noting that such Dark Eldar technology as has been recovered is almost without exception booby-trapped in a variety of ingenious and lethal manners.

Dark Eldar are classed by the Inquisition as an extreme danger. Under no circumstances are Imperial agents permitted to enter into dialogue or negotiations with them. Unfortunately their ability to imitate other, less hostile breeds of Eldar, if they so choose, leaves the Imperium vulnerable to their machinations. All Imperial war forces are under standing orders to treat Dark Eldar as hostile and act accordingly. Regrettably a campaign against the Dark Eldar cannot yet be instigated, for the Inquisition has yet to learn how their home realm of Commorragh may be reached and attacked.

According to the most reliable accounts, Commorragh is ruled by organizations known as Kabals, each comprising a number of Warriors and slaves under the command of a single Eldar, known as the Archon. The exact structure varies from Kabal to Kabal, but in most cases there is only a single Archon in any Kabal, with subsidiary leaders known as Dracons. Warriors are drawn from the strongest and cruellest of the Kabal's slave population, and if they survive and prosper may rise to become leaders in time. The leaders of the Dark Eldar are known collectively as Lords, though most affect whatever titles they please.

Kabals are almost always the instigators of raids against the Imperium, in which their Warriors are massed and formed into raiding parties in order to bring human captives. The exact fate of these captives is unclear: some are known to be killed in gladiatorial combat for the amusement of the Lords, some are simply tortured to death, some are put to work in similar fashion to the Eldar slaves possessed by a Kabal. A Lord's status seems linked to the quantity of slaves, Eldar and human, available to him. Mercenary groups, such as those known as Wyches, Mandrakes and Haemonculi, are often engaged to lend their support to raiding parties in return for a quantity of slaves and a percentage of the captives taken during the raid.

There are no known true laws in Commorragh, aside from the whims of its Lords. Some escapees speak of a so-called 'right of murder', in which one Warrior who kills a higher-ranked Warrior is entitled to his rank, but this seems to be more of a social convention designed to promote self-reliance and ambition. Murder of social superiors is apparently considered the primary course for improving one's position, and there seems no provision against such reprehensible acts.

One detail that is often mentioned by escaped captives, but has been dismissed by many Inquisitors as the ramblings of insane men, is that of the Lords of Commorragh feeding on the life force of others. Tales exist of Lords having the ability to literally draw the life out of captives, be they other Eldar or even humans. It is said that by this act a Lord can replenish his own life force, regaining youth and vitality. It is tempting to dismiss these wild stories, but there is some evidence to support them. Visual records of Dark Eldar Lords do suggest that they possess some method of reversing the progress of their own ageing, as the same Lord has sometimes been seen to be visibly more youthful than in previous sightings. Whether this strange, gruesome practice has anything to do with the value placed on captives by Dark Eldar, or if it is related in some way to the beliefs of the Craftworld Eldar regarding their 'waystones', is unknown.