The Warhammer 40,000 game world is a space opera that takes place in a gothic science-fantasy universe. Set approximately 40,000 years from now, most of the major storylines that provide the backdrop and history span over millennia.

Games are played between two or more players, referred to as "gamers", each of whom fields a group of units they have purchased, painted and assembled. The size and composition of the groups, referred to as armies, are determined on a points system, with each unit (figurine) assigned a number of points proportional to its worth on the battlefield (a better unit or model is worth more points). Before a game, the gamers agree on how many points will be used as the maximum army size and each assembles an army up to that maximum limit. The composition of these armies are usually constrained by rules contained within the Warhammer 40,000 rulebook, as well as in several army-specific codexes. Common game sizes are between 500 and 2,000 points and played on tables four feet in width and four to eight feet in length, but it is possible to play much larger games given the time and inclination (larger point battles tend to be played by multiple gamers on larger tables).
At the onset of each battle, a set of rules and goals, specific to that combat, are determined; these are collectively referred to as a scenario. Gamers have basic goals, which range from the capture of one or more objectives, to simply destroying the enemy. Additional rules may include fighting at night or other factors that affect troops' abilities. These scenarios may be straightforward and take only a half hour to complete, or they may be complex and require several hours to finish. A series of scenarios may be organized into a campaign, where two or more players fight against each other in a number of battles. These campaigns may feature their own special rules, and are typically tied together by a storyline, which might evolve based on the results of each scenario. Scenarios and campaigns are designed by Games Workshop and printed in the codexes, rulebooks or White Dwarf. Alternately, gamers may design their own scenarios or build new campaigns from premade scenarios.


Play is divided into phases where each player moves, shoots, and/or engages in close combat with various units. In the movement phase, a player determines the direction and distance individual units will travel. Some units can travel further than others in a single move, and terrain may inhibit movement. In the shooting phase, the player has the opportunity to make long-distance attacks with units that are within range of the enemy. In the Assault Phase, units may engage in close-quarters fighting with enemy units in close proximity. After one player completes all three phases play is turned over to the opposing player. Contingent events such as weapon hits and misses are determined by the roll of six-sided die and unit characteristics. A specialty die called a scatter die is used to determine deviation for less accurate events such as artillery barrages or reserve units deploying onto the battlefield through irregular means. Unlike some wargames, Warhammer 40,000 is not played on a hex map or any kind of pre-defined gameboard. Instead, units can be placed at almost any physical location on the table. Range between and among units is important in all three phases of play. Distance is measured in inches using a ruler. Determination of line of sight , is made at "model's eye view"—gamers may bend down to observe the board as model would. Victory is determined by points, awarded for completing objectives and/or destroying enemy units.

Battle between Imperial Guard and Tau with dice and terrain elements visible
Terrain is also an important part of play. Common household items like soft drink cans, coffee cups,styrofoam packing pieces, and pill bottles can be transformed into ruined cathedrals, alien habitats, or other terrain with the addition of plastic cards, putty, and a bit of patience and skill.

Modelling

Like Warhammer, Warhammer 40,000 involves both actual table-top play and the "meta-game" of preparing models and armies for play. For many gamers the preparation of models is sometimes more important than the actual gameplay itself. Gamers purchase the figurines from their local store and then assemble and paint them before they use them in battle. The painting itself lends a sense of authenticity to the owner of the figurines, indicating how serious he or she is about the hobby.  Depending on the number of units, it can take weeks or months to complete an army, this time may include modification of the original paint schemes and even model poses to personalize each army.