The populace of the Imperium is mostly Human. While there is the possibility of having Sanctioned Xenos operating under the watchful eye of a Rogue Trader, or perhaps Ordo Xenos Inquisitors of a more Radical bent, they are so rare as to be unknown by the common man.
Xenos and Abhumans
All Xenos are considered to be Unsanctioned unless they take the Sanctioned Xenos perk (see below).
Eldar (3) - your maximum Agility is raised to 5D. You naturally possess the Psyniscience skill. However, your alien nature makes people less likely to trust you - you suffer a -2 penalty to all Fellowship skills when used on a member of the Imperium.
Kroot (3) - depending on your Kindred and diet, you can raise one of your Stat caps to 5D, though you must drop another to 3D. For example, those who have battled Orks and eaten their flesh might gain added muscle mass, but find themselves unable to adapt to more refined social situations (5D Strength, 3D Fellowship). Or those who feed on Dark Eldar may find that their movement become almost preternaturally fast, but their inquisitive minds are dulled by vicious, almost animalistic dark instincts (5D Agility, 3D Intelligence). The GM is the final arbitrator of what is a suitable pairing.
Sanctioned Xenos (1) - while you are still hated, you are somewhat accepted amongst the Imperium. So long as you have your Sanctioning paperwork, and someone of suitable influence, you may enter Imperial space as a human, with some of the same rights. While many will still want you dead, the clout of Sanctioning and your powerful friend should help stay their hand. You lose the Unsanctioned Xenos Complication.
Far more common, especially in the theatre of war, are the Abhuman Races - offshoots of Humanity who have adapted to life on less Terra-like planets, and have seen their bodies change in response to environmental factors. While many are derided as mutants, most are "stable" mutations - developed over centuries, instead of the corrupt mutations shown by the followers of Chaos.
Ogryn (2) - you are one of the hulking Ogryn, massive Abhumans hailing from high-gravity worlds. Their natural strength is renowned, but many fall well below the normal intelligence curve of humanity. Your maximum Strength is increased to 5D, but your Intelligence cannot be raised higher than 3D. Note, an Ogryn with 3D in intelligence is still a mental giant amongst his race. You gain the Large Complication.
Ratling (2) - you are one of the tiny Ratlings, small, nimble Abhumans with a penchant for becoming snipers and cooks. Their small frame means that they are unable to fight as well in close combat as their squadmates, but their ability to sneak around unnoticed and plant a bullet in the eye of a fly from 50ft away more than makes up for it. Your maximum Agility is increased to 5D, but your Strength cannot be raised above 3D. You gain the Small Complication.
While not as pronounced as the changes seen in Abhumans, the variety of worlds the Imperium has colonised has led, through biology, psychology, and culture, to certain patterns in skill-sets of those from particular types of worlds. From the expert woodsmen of Feral Worlds to the edgy, fast-talking Hivers, these Home Worlds span the breadth of the Imperium - and will make a huge impact on a person's development.
Home World options cost 2 Dice at character creation, and cannot be taken at any other time. The dice granted by these Perks can take starting Skill dice above the usual 2D. Characters without a Home World Perk are considered general Imperial Citizens, born on any number of "standard" Imperial planets.
Dark Heresy Home WorldsHive World - gain an extra die to the Streetwise Skill, and a +1 bonus to Initiative rolls.
Feral World - gain an extra die to the Survival Skill, and a +1 bonus to your Soak Value.
Void Born - start each session with an extra Hero Point, but receive a -2 penalty to all Fellowship Skills when used against non-Void Born.
Forge World - gain an extra die to the Tech-Use Skill, and a +1 bonus to any rolls to repair or maintain technology.
Schola Progenium - gain an extra die to the Command Skill, and a +1 bonus to any rolls to resist abilities that influence, control, or read thoughts and emotions.
Rogue Trader Home Worlds
Noble Born - gain an extra dice to the Diplomacy Skill, as well as a +1 to Fellowship rolls in high-society situations.
Death World - gain an extra dice to the Survival Skill, and a +1 bonus to all Strength rolls to resist poisons or harsh climates.
Frontier World - gain an extra dice to the Wrangling Skill, and a +1 bonus to all Strength rolls to resist the effects of fatigue.
Footfallen - gain an extra die to the Persuasion Skill, and a +1 bonus to all rolls to do with knowledge of the Koronus Expanse (its legends, lore, power groups, etc).
Fortress World - gain an extra die to either the Pistols or Rifles Skill, but gain a -1 penalty to all Fellowship Rolls regarding non-warfare topics.
Battlefleet - gain an extra die to the Pilot Skill, and gain a +1 bonus to all rolls related to commanding subordinates on a starship.
Penal World - gain an extra die to the Intimidate Skill, and gain a +1 bonus to all rolls relating to the criminal underworld.
Child of Dynasty - gain either an extra die to the group's Profit Factor, or an extra die to Starship Creation, and a +1 bonus to all interactions with high authorities.
Small - This is a Racial Complication. Player Characters gain this only by the Ratling Perk. Small characters receive a -5 penalty on all Might skill checks, Might based damage rolls, Block, and Parry. This penalty doesn’t apply to Stamina, healing, and resisting damage. This penalty doesn’t apply when fighting a Small or Tiny creature. Earn 1 bonus CP each session.
Large - This is a Racial Complication. Player Characters gain this by the Ogryn Perk or others. Large characters gain all the negatives of being Scale +2D, but no benefits (so, they are easier to hit and may find it harder to hit smaller creatures). They also require gear to be tailor-made to their bulk (such as the Ogryn Ripper Guns, or far larger armour than usual). They may also have trouble fitting into vehicles or other places sized for an average human. Earn 1 bonus CP each session.
Unsanctioned Xenos - This is a Racial Complication. Player Characters gain this only through the various Xenos Perks. You are a source of hatred within the Imperium - you suffer a -2 to all Fellowship skills against those who hold the Imperial Creed, and many people will want to shoot you on sight. Gain 1 bonus CP each session.