Warhammer 40,000 , also called 40k, is a table-top game and fictional setting made by Games Workshop, in which model armies fight against each other on miniature terrain.

Rules 
Two or more players are needed for a game. Each player takes turns to use their army in several phases: command, movement, psychic, shooting, charge, fight and morale. It is played using dice to decide what happens as a result of player decisions, and a ruler to measure distances between units. Each model has ratings for statistics such as "ballistic skill" (shooting), "weapon skill" (hand-to-hand combat), "toughness" (how hard they are to hurt), "leadership" (how brave or disciplined they are) and "armor save" (how effective their armour is at preventing damage). Models move freely around the table instead of being restricted to the cells or spaces of a traditional board game, and may move into or out of cover (called Terrain).

Each player builds an army of miniatures by choosing units from the appropriate army list (called a "Codex"). Missions often impose restrictions on which units must or must not be included. Models may also be equipped with different weapons and equipment (such as armour, shields, grenades and jet packs), which modify their statistics in many ways. For example, a model may be equipped with a Boltgun (a standard infantry weapon that can fire while moving), a Heavy Bolter (to take down lots of enemy infantry at long range), a Lascannon (to take on enemy tanks) or could give up ranged weapons in favour of swords, axes or power fists (various hand-to-hand combat weapons).

Setting 
Warhammer 40,000 is set in the 41st millenium, a science-fiction future version of the real galaxy. Humanity has spread throughout the galaxy and encountered many Xenos (alien) races, most of which are extremely hostile. While humanity once dominated the galaxy, events such as an AI rebellion and major civil war have reduced them to a dying empire barely clinging to power. Artificial intelligence tends to become too smart to coexist with it's creator so is generally banned by most factions, who instead rely on manual labour.

There is an alternate psychic reality called the Warp, that mirrors the material galaxy and allows for psychic powers (similar to magic in fantasy settings), psychic beings (such as Daemons) and interstellar travel. The Warp is an unstable dimension fed by the emotions of various races in the galaxy, and it fluctuates in strength it can greatly help or hinder various factions.

The setting is considered "Grimdark" which means it is a very bleak and violent setting, with little hope for lasting peace between the factions. This means any faction may fight or ally with any other faction while remaining consistent with the story, which allows players to tell stories about the games they play.

Factions 
There are many factions in the setting, both large and small. Only the largest factions have official models from Games Workshop, though many players paint or modify their models to represent one of the minor factions. Players often make their own stories and rules to support their minor factions, though this is usually not supported at official Games Workshop events (such as tournaments).

Major factions supported by Games Workshop include:

Imperium of Man 
The Imperium of Man is the civilization that today's humanity has become. The Imperium is ruled by the Emperor of Mankind, an immortal man with the most powerful psychic abilities. Unfortunately he was badly wounded during the Horus Heresy (the largest Imperial civil war), and is no longer able to lead humanity. The Imperium is a very spread-out civilisation, 

 Astra Militarum (Imperial Guard): The large armies of normal humans. They use basic but reliable equipment, such as the icon Lasgun (a laser rifle) and Leman Russ battle tank. Regiments of Imperial Guard are raised from planets all over the Imperium, so have a wide variety of appearances and tactics. The Imperial Guard is reliant on the Imperial Navy to transport it between planets. Players can also use these models to represent more minor human military factions, such as Planetary Defense Forces (PDF), traitor human armies or Imperial Navy troops.
 Adeptus Astartes (Space Marines): Space Marines are genetically modified humans, that are larger, faster and stronger than normal humans. They have extra organs that allow them to heal quickly, breathe underwater, spit acid, resist poison, etc. They wear advanced powered armour that both enhances their strength (allowing them to carry heavy weapons) while also providing protection similar to a light armoured vehicle. Space Marines are organised into 1,000 "Chapters" of 1,000 marines each, to prevent them forming a threat to the Imperium's political structure. Space Marines can live for a very long time (some are centuries or even millennia old), and become very skilled warriors due to their experience. Unlike the Astra Militarum, Space Marines are allowed to keep their own space fleets.
 Adeptus Sororitas (Sisters of Battle): The Sisters of Battle are an all-female order of warriors under control of the Ecclesiarchy (the Imperial church). The head of the Ecclesiarchy rebelled against the Imperium millenia ago, and was banned from using "Men under arms"; the Sisters of Battle exist on a legal technicality, as they are not men. They are very pious and carry out many religious wars in the Emperor's name.
 Adeptus Mechanicus: The Mechanicum is a whole civilisation dedicated to rediscovering old human technology (which they believe is holy), and exists alongside the Imperium. The Imperium has made a deal with them to provide all the materials and knowledge it can, while the Mechanicum in turn provides the machinery and war materiel the Imperium needs to remain in power. Adeptus Mechanicus members are often highly modified with bionic augmentations such as mechanical limbs, electronic eyes and brain computers. The Mechanicum also keeps control of the Titans, giant mechs that are humanity's most powerful ground-based war machines.
 Imperial Knights: Mechs that are smaller and simpler than Titans but still very powerful. They are owned and used by the Knight Houses, families that control feudal human worlds.
 The Inquisition: A large organisation of secret police, dedicated to fighting specific threats to humanity rather than large wars. The Inquisition has three main orders: Ordo Malleus to investigate Daemon activity, Ordo Xenos to investigate aliens and Ordo Hereticus to look for traitors, heretics and mutants. The Inquisition cannot be played as it's own army in the game, but small units to represent it's agents may be added to many other human factions.

Chaos 
The forces of Chaos are those influenced by the power of the Warp. The Warp is a corrupting influence on most species, leading them to unpredictable behaviour. Chaos feeds off the emotions of the various races in the galaxy, and the strongest emotions combine to form powerful Warp beings called the Chaos Gods. The strongest four are: Khorne (anger, violence, hatred), Tzeentch (scheming, plots, change), Nurgle (entropy, disease, physical corruption) and Slaanesh (lust, greed, excess, pain, pleasure). The Chaos sub-factions may align with one, several or all of the Chaos Gods (known as "Chaos Undivided").

 Chaos Space Marines: These are Space Marines that have turned away from the Imperium for whatever reason. Many start with simple piracy, but slowly turn to the Chaos Gods for resources to support their operations. The first Chaos Space Marines occurred at the end of the Horus Heresy, a large civil war that place ten thousand years ago. Chaos Space Marines are generally in charge of the other Chaos forces, unlike in the Imperium.
 Daemons: Daemons are warp beings of varying power, too weak to be considered Chaos Gods. The normally need to be summoned by a psyker to enter the material galaxy, but in areas where the Warp is very active they can sometimes cross over by themselves. Daemons have various powers depending on which Chaos God they align with.
 The Lost and the Damned (traitor humans): There are many large groups of Chaos-aligned humans, though many are there through enslavement rather than choice. They are generally less well-organised than their Imperial equivalents, though with help of the Dark Mechanicum they are often just as powerful. They can be represented in the game using the rules for the Imperial Guard.
 Dark Mechanicum: The traitor counterpart to the Adeptus Mechanicus. Due to their lack of resources and equipment, they often incorporate Daemons in place of other components, leading to powerful but often-uncontrollable machines.

Aeldari (Eldar) 
The Eldar are an ancient, powerfully psychic, technologically-advanced race, resembling the elves of many fantasy settings. They were once the most powerful faction in the galaxy, but their self-indulgence and debauchery led to their downfall via the creation of the Chaos God Slaanesh. The Eldar has splintered into many sub-factions, some of which share alliances and utilise the same types of equipment. The Eldar were responsible for the construction of the Webway, a way of traveling around the galaxy without risking exposure to the Warp (though it is now in disrepair). Some factions can make use of "Spirit Stones" that collect an Eldar's soul when they die to prevent it being captured by Slaanesh; these can then be used to operate machinery such as spaceships or combat mechs.

 Asuryani (Craftworld Eldar): An entirely space-borne faction of the Eldar, the Asuryani live aboard their gigantic spaceship-cities called "Craftworlds". The various Craftworlds are independent of each other, with no overall leader directing them. Asuryani dedicate themselves to various "Paths" (like having careers or learning skills in humanity) such as becoming an artisan, mariner (space sailor), leader or warrior. Some Eldar stay on one path their whole life, while others change between them as desired.
 Exodites: The Exodites are Aeldari that have rejected advancement and technology, having abandoned the Craftworlds prior to the Eldar's fall to Slaanesh. The Exodites live on planets rather than spacecraft, and make use of "World Shrines" to capture their souls in an artificial afterlife instead of spirit stones.
 Harlequins: Harlequins are Eldar aligned with the god "Cegorach" (the "Laughing God"), and mix their combat skills with theatrical, acrobatic performances. They began as a group to warn of the impending fall of the Eldar, and now continue their role as historians of the Eldar race. The Harlequins live in the remains of the Webway, and when they emerge for combat they are known for fast, fluid, dance-like motions.
 Ynnari: The Ynnari are a new group of Eldar with members from all factions (even from the Drukhari). They worship the young Eldar god Ynnead, who the think may be the last hope of saving the Eldar race from extinction. They live aboard fleets of spaceships, and focus most of their efforts against the forces of Chaos.
 Drukhari (Dark Eldar): The Drukhari are the remains of the self-indulgent Eldar that led to the fall and the creation of Slaanesh. They are longer-lived than other Eldar, though this requires them to consume souls to extend their lives. The Dark Eldar suffer from "The Thirst", which is the need to capture other beings, torture them and consume their souls. Unlike other Eldar, psychic powers are rare. The Drukhari live in the twisted city of Commorragh, hidden within the Webway. They conduct regular raids into real space to capture slaves for their souls.

Orks 
The Orks are an artificially-engineered race with a crude but brutal nature, and provide much of the comedy relief for the setting. They may well be the most numerous race in the galaxy, but their highly fractured clan structure means they often fight amongst themselves rather than work together. Orks are the main sub-species of "Orkoids", which vary from the tiny child-like Snotlings up to the massive dinosaur-like Squiggoths. Orks require competition and violence to live as it makes them stronger, and Orks that do not fight will weaken and die. Orkoids are actually a fungus and spread via dropping spores instead of sexual reproduction, making them difficult to wipe out as their battlefields soon become spawning grounds for new Orks. Orks have a lot of knowledge encoded into their DNA such as medicinal care (Dokz) and engineering (Mekz), of which the most skilled are called Oddboyz. Rarely an Ork warboss will become powerful enough to declare a "Waaaagh!", which unites many clans into a crusade for fighting and looting. A "Waaaagh!" will often burn out by itself, as the Orks eventually turn to infighting.

Necrons 
The Necrons are an ancient race of mechanical warriors resembling skeletons, who used to be organic beings called the Necrontyr. The Necrontyr were tricked by the godlike beings called the C'tan, who gave them powerful weapons and promised them eternal life. Once the Necrontyr conquered the galaxy, they realised "eternal life" meant being turned into machines without souls and individuality. Now called Necrons, only the strongest kept their personalities and emotions. The Necrons turned on the C'tan and shattered them, capturing them in Shards to use as weapons. The fight against the C'tan had weakened the Necrons, so they chose to enter stasis on their Tomb Worlds, to sleep until the galaxy was one again full of life for them to harvest. The Necrons have slowly started to awaken in the 41st millennium, ready to strike out into the galaxy once more. Necrons are made of a substance called "Living Metal" that is very resistant to damage, but also allows them to repair themselves when destroyed. When too many Necrons of an army are defeated the rest "Phase Out" by teleporting back to their tombs, to rebuild their strength to fight another day.

Tyranids 
The Tyranids are an insect-like race that come from outside the Milky Way galaxy. They are formed into large Hive Fleets, collections of gigantic organic spaceships that can birth smaller creatures to fight on planets. The Tyranids are united and controlled by the Hive Mind, a psychic, intelligent consciousness that directs their actions. The Tyranids have been seen as instinctive by other factions in the galaxy, but they are slowly realising the Hive Mind is smarter than a mere insect. So far three main Hive Fleets have entered the galaxy (Behemoth, Kraken and Leviathan), but there are many smaller fleets formed from splinters of these main fleets. The Tyranids do not use any technology, relying instead on symbiotic organisms; for example, a Tyranid "gun" is actually a separate organism that can spit acid, give birth to flesh-eating beetles or project hardened spikes of bone. One challenge in fighting the Tyranids is the "Shadow in the Warp", and effect of the Hive Mind that dampens psychic powers, interstellar travel and communications. The Hive Mind is driven by eternal hunger, meaning the Tyranids only goal is to consume all organic material in the galaxy before moving on. When Tyranids attack a planet they consume all life, drink the oceans and suck up the atmosphere, leaving only airless rocks behind. The Hive Mind is capable of rapid evolution and is able to absorb the DNA of enemies they consume, meaning they are a constantly changing threat.

Genestealer Cults 
Genestealers are an important Tyranid lifeform, who travel far ahead of the Hive Fleets to prepare worlds for invasion. Genestealers land on a planet and infect it's inhabitants, slowly building a "Genestealer Cult" that destabilizes any resistance to the approaching Hive Fleet. Infected members of the cult believe the approaching Tyranids are their salvation, but they are instead attacked and consumed like any other lifeform.

T'au Empire 
The T'au are a small and very young race, only a few thousand years old. They are very technologically gifted, with lots of scientists and engineers. The T'au are formed into four major Castes: Fire (warriors), Earth (scientists, engineers, farmers), Water (traders, bureaucrats, diplomats) and Air (pilots, spaceship pilots). A fifth leader caste, the Ethereals, control the rest of the T'au via some unknown method (possibly pheromones). The T'au believe in the "Greater Good", a philosophy where they all work together to build a more successful, easier future. The T'au do not have any psychic abilities and have very little psychic presence within the Warp, making them largely immune to Chaos. Instead of these abilities, the T'au use their powerful technology to compete with the larger factions. One feature of the T'au is their willingness to work with or subsume other races instead of fighting them, leading to a big variety of units they can deploy. The T'au prefer to fight at long-range, and rely on other races to fight in close combat.

Allied/Subsumed races 
The T'au work with many other races, the most major of which are as follows:
 Kroot: A humanoid race that may have original been bird-like. The Kroot are able to direct their own evolution, leading to many sub-species such as the dog-like Kroot Hound or the ox-like Krootox. The Kroot are known to work as mercenaries for other factions, not just the T'au. They are used in close combat due to their fast movements and excellent hand-to-hand skills.
 Demiurg: A space of short, squat, space-based miners and traders.
 Vespid: An winged, insect-like race that did not initially want to ally with the T'au. The Ethereals provided them with "communication headsets" that mysteriously made them compliant and co-operative. They operate in war as scouts and rapid-reaction troops.
 Nicassar: A highly psychic race in hiding from the Imperium, the Nicassar allied with the T'au for protection. They have fast, maneuverable ships that help the T'au explore new star systems.
 Gue'vesa (humans): The Gue'vesa are humans that have either been convinced to join the T'au Empire by the Water Caste, or who have been captured during wars between the T'au and the Imperium. They are given a relatively high degree of freedom by the T'au, and work together in combat to make up for each other's weaknesses.

Hobby 
A key feature of Warhammer 40k is the assembly and painting of the miniatures and terrain. Model kits are made from either plastic or resin, and can often be assembled with a variety of options (poses, weapons, equipment, etc). Models are then painted in the colours of the player's choice, which can either match a faction in the setting or be a custom creation. Players also assemble or make terrain, to place on the tabletop to create a battlefield. Some people do not play the game at all but like the models, so are interested in 40k only for the modelling aspect. Others are keen on coming up with the best armies and strategies, and compete with one another in tournaments.

Supporting games 
There are many supporting games that use the 40k setting, usually with some or all of the major factions listed above. These games may sometimes re-use the models and statistics of the main game, or may instead have unique models and rules. Examples include:

 Battlefleet Gothic: Spaceship combat, the future equivalent of naval warfare.
 Aeronautica Imperialis: Aerial dogfighting between aircraft.
 Adeptus Titanicus: Fights between giant mechs.
 Kill Team: Combat between very small teams of models (typically 5-15 each), representing special forces operations.
 Necromunda: Combat between various gangs in the seedy underworld of a single, large human city called a "Hive".
 Horus Heresy: Battles mainly between Space Marines, set during a large human civil war.

References 
 http://uk.games-workshop.com/default.aspx 

Games
Modelling

no:Games Workshop#Warhammer 40,000