Xenos
Xenos is a Greek word which can mean "stranger". In W40K "xenos" means "alien" from the perspective of mankind.
The major alien races (those featured as actual armies) pose a considerable threat to the survival and continued dominance of mankind; others are relatively trivial.
The major alien races are the Orks, the Eldar and their sadistic kin the Dark Eldar, the Tyranids, the Necrons, and the Tau.
The Imperium is highly xenophobic and not given to ideas of live and let live. Mankind has dropped concepts of peaceful co-existence in favour of simple survival, after the Dark Age of Technology - a time when non-aggression pacts were signed with many alien races, even though they could have simply been wiped out. Part of Imperial Creed is that all aliens posing a threat to mankind's survival must be rendered powerless, generally meaning they must be destroyed. The Imperium however, is not so simplistically genocidal that even nonthreatening alien species confined to only a single world are subject to extermination campaigns. Aliens - along with mutants, heretics and deviants - are all considered enemies of mankind - for they threaten the very survival of the human race.
Many new alien races and civilizations are discovered by Imperial Explorators every year. For the most part these aliens are ignored, contained, or if they present a threat to mankind or the Imperium, eradicated. Throughout its history the Imperium has fought many long wars with dangerous alien species. In most cases the Imperium has eventually won, but in some, the threat has only been managed to be contained.4
Although friendly dealings with aliens is almost unthinkable, Rogue Traders are allowed to barter and trade with aliens.
Contents
Military alliances
Despite all the fear and hatred, on certain occasions short-termed military alliances have been established with the Eldar. These temporary alliances are somewhat uncommon but not unheard of. Usually they are made against a mutual threat like the forces of Chaos, the Tyranids, or even the Orks. The Imperial Navy, units of the Imperial Guard, and even detachments of Space Marines have, on certain occasions, fought beside Eldar forces. A fine example for this is the Gothic War, during which the Imperium allied itself with the Eldar of the Craftworld An-Iolus against the forces of Abaddon the Despoiler. No temporary alliances with the the Tau have been made, but short-termed truces have happened.
Secret pacts
Some human organizations like some factions of the Inquistion, individual Navigator families, the Illuminati brotherhood, etc. even have certain secret dealings and alliances with the Eldar. All these agreements are always a carefully guarded secret as they would be considered treason by other more conservative factions of the Imperium. One such pact is the Coven of Isha.
Individual cases
Certain individuals, like Captain Gabriel Angelos of the Blood Ravens have had friendlier contact with certain Eldar. The Blood Ravens chapter in particular has had unclear contacts with the Eldar throughout its history. This is for obvious reasons kept secret by all parties involved.
Trade, smuggling, mercenaries, treason
Unlawful friendlier contact on a larger scale can happen, as some Imperial governors simply ignore Imperial law if the potential rewards are too great and will trade with some xeno races. Many items of xeno origin are smuggled into, and inside of, the Imperium. Exotic weapons, tomes of knowledge, poisons, certain xeno devices to dispose of one's rivals, etc seem to be craved by certain members of the jaded elite and seem to be commonly used in some quarters. A known example is the jokaero death spider which uses zarthax, one of the deadliest poisons in the galaxy1. Certain imperial factions use xeno weaponry on ocasion.
Some governors have even hired xeno mercenaries to maintain their grip on power.
The Tau deliberately foster such developments, trading with nearby Imperial systems and preaching the ideals of the Greater Good. As a result a very small number of Imperial governors on the frontiers of the Ultima Segmentum have recently seceded from the Imperium, pledging their allegiance and the loyalty of their respective worlds and star-systems to the Tau empire.
xenos and Chaos
The relationship between Chaos and the individual Xeno race/species varies from case to case. Some are completly immune. Others appear to be largely immune to Chaos corruption, although much of this immunity is of social nature. Others have been completely corrupted.
List of all known species
Old Ones
The Old Ones seeded life on many planets, fostering and changing many of the known inteligent species. Some races remember them as creator-gods or something similar.
Orks
The Orks are divided along tribes, and it is unknown if these tribes are sub-races or mere cultural divisions. Orkdom also includes the somehow related smaller Gretchin race and the even smaller Snotling race. Squigs are the product of captured Orks who were changed by the Tyranids.
Eldar
The original Eldar culture became more and more decadent and influenced by Chaos. After the Fall of the Eldar this race fractured along cultural lines. Those who managed to flee to Craftworlds underwent a major social reform but retained the original name Eldar, sometimes being called Craftworld Eldar. The Exodites had left Eldar civilization before the Fall and adopted a somewhat more hardier, primitive, and barbaric life-style. The Harlequins are travelling actors who perform ritual plays on many craftworlds and Exodite worlds. The Dark Eldar are a feared renegade faction, despised by all the others. They seem to hate them in return, and encounters usually lead to deadly confrontations.
Tau
The Tau empire includes several completly unrelated species who have been conquered or convinced to join the Greater Good (i.e. the Tau empire). The Tau race is divided by a Caste System and the castes are in fact sub-races of the Tau species. The same happens with the Kroot who call their sub-races Kindred. It is unknown if the Demiurg are full members of the Tau empire, allies, or mere trading partners.
Tyranid
The Tyranids are several related races who share the same conscience, the Hive-mind, and new races are bred all the time. The Genestealers serve as the Tyranid scout and infiltrator race. Other races are listed in: Species of Tyranid.
C'tan and Necrons
The four C´tan are 'star-vampires inside a material form' and are the gods of Necron. The Necron do not truly life in most common understanding of the word being quite similar to the 'Undead'.
Minor races
The following listed Xeno species seem to live isolated from each other and are not allied with any other species as far it is known. However some of them work as mercenaries, and most despise the xenophobic Imperium. The Imperium has struck severe blows to many of them, conquering or destroying many of their worlds.
- Cythor Fiends
- Hrud
- Hykosi2
- Jorgall2
- Lacrymole
- Loxatl, who fight along Chaos forces as mercenaries.
- Megarachnids, who may be already extinct.
- Nekulli
- Saruthi, who have been completely corrupted by the Necroteuch, a tome of Chaotic knowledge.
- Scythians
- Tarellians3
- Thyrrus
- Galgs3
