Xenos worlds are non-human and non-Imperial worlds inhabited by alien races. Most alien races occupy only a single world or a small group of worlds. The majority of aliens are comparatively primitive, peaceful or powerless, and of little interest to humanity. Only a few alien races are powerful, aggressive and possess technology which rivals that of the Imperium. Of these, the most common are the Orks, Eldar, Necrons and Tau.
White Dwarf 139 (UK) (page 9) states that "Humanity is but one of many races in the galaxy. However, none are so widely distributed or so numerous as humans." Contradicting this however, several sources (including Codex: Orks (2nd Edition) page 4) clearly state that the Orks are the most widespread race in the galaxy. A possible compromise of these two opposing statements would be that the Orks are the more numerous race but are split into many fragmented factions, whilst the Imperium is the largest cohesive empire.
The Necrons also believed to be even more widespread than both Orks and Humanity as on (page 17) Codex: Necrons (5th Edition) it says that "These Tomb worlds represent only a handful of the many millions spread throughout the galaxy." and on (page 8) that "even now, at the close of the 41st Millennium, billions of Necrons still slumber in their tombs, silently waiting the clarion call of destiny" which shows that the Necrons could possibly outnumber every other race in terms of planets and numbers.
|Worlds of the Galaxy|
|General||Dead World • Death World • Desert World • Ice World • Jungle World • Ocean World • Derelict Worlds • Chem Worlds|
|Imperium||Adeptus Astartes Homeworld • Agri World • Cardinal World • Cemetery World • Civilised World • Feral World • Feudal World • Frontier World • Forest World • Forge World • Fortress World • Hive World • Industrial World • Knight World • Labyrinth World • Mining World • Paradise World • Penal World • Quarantined World • Quarry World • Repository World • Research Station • Sentinel World • Shrine World • Swamp World • War World • Hub-Fortress|
|Chaos||Daemon World • Hell Forge • Fallen Knight World|
|Xenos||Xenos World • Exodite World • Tomb World • Maiden World • Crone World • Ork World • Tau Sept • Craftworld|