Warhammer 40K, properly titled Warhammer 40,000 (and formerly known as Rogue Trader), is a miniatures wargame in 35mm scale, set some 38000 years in the future, in and around a interstellar Imperium beset by foes from without and within, designed by Rick Priestley, Andy Chambers, Gav Thorpe, Ian Pickstock, and Jevis Johnson (in the current incarnaton) and published by Games Workshop.

A quick note: While the creators of this game are British, I am not, so I will not be referring to "daemons," "armour," or any other such Britishisms.

Described by some as an addiction, or even a way of "separating [adolescent boys] from as much of their money as possible, as fast as possible," in the words of Dhericean, it cannot be argued that the game is not a raging financial success in both the US and the UK, now on its third edition, with countless spin-offs.

While the setting isn't riveting science fiction, with stoic, heavily-armed elite troopers, a slavering, insectoid race, elves in space, and whatnot, a new player could certainly expect major cliches like an oppressive, galaxy-spanning Imperium that controls almost all of mankind. What that new player would certainly not expect is that the oppressive Imperium (it's never called an empire) just happens to be the good guys.

"In the grim darkness of the future, there is only war."

The Imperium of Man is lead by the eponymous Emperor of Mankind, trapped for the last 10,000 years in his Golden Throne, the stasis-chamber/crypt that has sustained him since the events of the Horus Heresy, and spans hundreds of thousands of occupied worlds of varying poulation, with the capital on Terra. The Imperium of Man is represented, in the game, by three forces: the Space Marines, the Imperial Guard, and the Sisters of Battle (who are a part of the Adeptus Ministorum). (There's also the multi-story mecha of the Titan Legions, the independant operators of the Inquisition, the techno-cultists of the Adeptus Mechanicus, the assassins of the Officio Assassinorum, and others, but they're generally bit players in the game.) The chief religion of the Imperium, of course, is Emperor-worship, ably justified by the fact that the Emperor is very nearly a god, with the battle cults of the Space Marines and the Cult of the Machine God (the religion of the Adeptus Mechanicus) only tolerated within strict limitations. This limitation, of course, is more than spiritual; the alternative is quite malevolent, in that it wants your soul, and it's quite willing to go and abbreviate your lifespan in the pursuit of that goal.

Chaos refers collectively to the Chaos Gods and their followers, all of whom make the Inquisition and the practice of Exterminatus (the scouring of all life on a planet to prevent the spread of Chaos, Tyranids, Orks, whatever) positively friendly. The Chaos Gods each represent some aspect of evil. Khorne, the Blood God, feeds on violence and destruction, and his followers strive to spill blood in his name. (They have such heartwarming battlecries as "BLOOD FOR THE BLOOD GOD!" or "SKULLS FOR THE THRONE OF KHORNE!") Nurgle, the God of disease, has followers who spread illness in battle and elsewhere, and is well-known for Nurgle's Rot, a bloating, always-fatal disease that can sometime transform its victims into mockeries of his demonic Plaguebearers (until the disease kills them). Tzeentch (pronounced "Zeench") is the God of change. Apparently Change encompasses pastel-colored demons and bolts of psychic energy. Last, but not least, is Slaanesh, the God of pleasure, whose followers tend toward claws and phallic imagery. Besides demons and cultists, the main force of Chaos consists of Chaos Space Marines, the corrupted former defenders of humanity.

Of course, humans (and those that used to be human) aren't all there is to see. The Orks, for example, are, well, typically green-skinned, square-jawed, over-muscled, and under-witted, fitting nicely into the generic fantasy/sci-fi orc template. Warhammer 40K orks, however, have a penchant for weird science and salvage, however, leading to the interesting spectacle of ramshackle ork "battlewagons" built from several other vehicles found on the battlefield and bolted together. Explanations for their bizarre mechanical feats and spectacular regeneration tend to pseudoscientific genetic (Orks have twisted triplets for DNA, for example) or psychic (Ork weapons and technology work because all the Orks collectively believe that they do). It's obvious that the Orks are a favorite of the designers, since the rules and stories are always delightfully bizarre, with a tendency towards self-immolation. (Ork weapons also have a notable tendency to explode.)

Just because every setting needs a mysterious dying elder race with pointy ears, there are the Eldar, a, well, mysterious dying race with pointy ears. They travel about on planet-sized starships known as "craftworlds" and follow the leadership of their psyker Farseers. Eldar are a dying race (due to the events of the Fall of the Eldar), and adhere to rigorous "paths", or lifestyle/careers, to shield themselves from sinking into the hedonism of the Fall. That, and they trap the souls of their dead in soulstones, which, in time of need, can pilot robots and Wraithlords and tanks and such.

Following in the Warhammer 40K tradition of ruthlessly milking any cliche that sits still long enough, there's also a hideous slavering race of Giger-esque insectoid carnivores, hive mind and all. The Tyranids are, well, a hideous slavering race of Giger-esque insectoid carnivores, ones with a tendency to land on a planet, consume all of the biomass, the air, and water, leaving behind a scoured rock. While the form of the creatures themselves tend to vary (in the game, there are rules for making up your own "bugs"), they all tend towards wiry muscles, bony plates, acid spitters and giant claws.

There are also some more recent additions to the 40K universe, retconned nicely into the fabric of the setting. (To be fair, the creators of WH40K do a good job of leaving loose ends, and of weaving new races and new additions into the milieu]) There are the debased Dark Eldar, the survivors of the Fall of the Eldar, adhering to the old ways of violent, self-centered hedonism. The Tau (and their mercenary Kroot) are the single optimistic race in the setting, with their "modern" tactics, positive outlook, and heavy weaponry. Thing is, they're also hopelessly outmatched. The newcomer Necrons are a blend of Terminator-style indestructible robots and Egyptian/Stargate Elder Forces, and generally dislike all living things just because they happen to be living.

That's the setting. Now, as for the rules...

In the third (and latest, released in 1998) edition, the game emphasizes the bread-and-butter squads of each army, with army composition that limits any attempts to focus in a certain area of specialized troops. While it's difficult or even impossible to concentrate your army on heavy, immobile weaponry, it's not hard to take an army of mostly specialists, as long as they were different kinds of specialists.

The rules have little to nothing in common with most historical wargaming. Lethality of weapons is extremely low, personal armor is often highly exaggerated, ranges are pitifully short, and morale effects are generally not a big deal. This makes for a forgiving and highly dynamic game, but will definitely annoy anyone who looks for a high level of realism in their wargaming.

The actual tactical dynamics of the game tend heavily into run-and-gun close range combat, with an extremely heavy emphasis on melee. Most armies will spend at least some time in hand-to-hand combat, and having a way to initiate, survive, or prevent melees is quite important.

The rules, unfortunately, follow the Games Workshop tradition of vagueness. A lot of the rules have had to be clarified or even rewritten in later supplements or in the house rag/company magazine, White Dwarf. Especially bad are the rules for melee and for assigning casualties. The game is best played with a group of experienced players, because the rules aren't neccessarily intutive, it's just that the rulebook's presentation is often unneccessarily vague.

Info on previous editions of the game can (or will, if not yet noded) be found in Rogue Trader or Warhammer 40K, Second Edition.

Sources: Warhammer 40K Third Edition Main Rulebook, my own good memory, the Games Workshop node, and a pile of of White Dwarfs yay high.