The Tau have advanced rapidly since their first encounter with the Imperium of Man in the 35th millennium, rising from a hunter-gatherer level of technology to a starfaring race in less than six thousand years. Tau society has also advanced rapidly, from warring tribes to a unified caste system working towards common goals, known by the Tau as Tau'va, The Greater Good.
As well as the five castes of the Tau, multiple alien species are incorporated into the Tau Empire; the most significant of these being the Kroot and Vespid although many other races, including the space faring Nicassar and the mercenary Tarellian Dog Soldiers are members. In addition, human auxiliaries (Gue'vesa in the Tau language) are sometimes seen to be aiding the Tau as well.
The Tau were the fourth army to receive a Codex updated for Fourth Edition rules (Codex: Tau Empire - Hoare, 2006). Additional rules for the Tau appear in a Forge World Imperial Armour rules supplement (Imperial Armour Volume Three - The Taros Campaign - Kinrade, 2005).
The Tau are humanoid in shape, although they have hooved feet and four-digit hands (three fingers and one thumb). Their skin is grey-blue (although this can vary in pigmentation between worlds), rough in texture, leathery, and exudes almost no moisture. Their faces are flat, wide around the eyes, with an "I"-shaped indentation running from the centre of the forehead to where a human's nose would be. Tau vision is considered slightly superior to humans - their visual spectrum extends a little more into the ultraviolet and infrared wavelengths. However their pupils do not dilate giving poorer depth perception and slower focusing reflexes than Humans. The olfactory organs are inside the mouth. Physical strength and size varies between castes, with the Fire Caste being among the largest of the Tau.
Only two identifiably female Tau have ever been illustrated. The first, Commander Shadowsun, appeared to have a more human face than male Tau; being smoother and sleeker with larger eyes, a nose-like facial feature and a "Y" shaped facial slit. It is not known, however, whether Shadowsun is representative of all female Tau. The second, the subject of an imperial dissection, had the facial characteristics of a male Tau.
The Tau do not possess psykers (indeed, their minds barely register in the warp at all) and as a result have little knowledge of the Immaterium beyond its existence. This gives them some level of resistance to warp-based powers affecting the mind, but it offers little, if any, protection against physically-manifested offensive powers. They are largely unaware of the perils of the Immaterium and for this reason the Tau have conducted research into the Warp on Medusa V, however, the conclusion was reached that further research was unfeasible, and that "the Warp is no place for the Greater Good and is best left to those foolhardy races who cannot pull back from that terrible realm." Also with no other knowledge of the warp none of their starships are fitted with true "Warp Drives" meaning that all worlds the Tau have colonized are relatively close to one another.
Ethereal Caste members also have a diamond shaped bony ridge on their head. It is believed by Imperial scholars that they exert a pheromone-based control over the other castes, a theory supported by Ordo Xenos examinations of dead Tau Ethereals in the Games Workshop book Xenology.
While the Age of Apostasy troubled the Imperium and its army, the primitive tool users that would one day become the Tau began to spread out from the plains as hunting grounds grew scarce. Each tribe adapted to their new environments with significant speed; while those that migrated to the river deltas developed their metalworking and agricultural skills, the groups that remained on the plains became skillful and aggressive hunters.
Along with the rapid adaptation came an equally rapid level of technological development. The Tau quickly came to use black powder weapons and stone fortifications. Soon, the tribes that inhabited the plains and the mountains fell into conflict with the groups dedicated to agriculture and trade. Vast inter-tribal wars were fought across the main continent, lasting for years at a time. Thousands died on each side of the conflict, while squalid conditions and lack of access to fresh food and water created a plague that killed more Tau than were dying in the wars.
By the end of the 37th millennium, the Tau were on the verge of wiping themselves out. At the same time as war and disease reached their most deadly levels, strange events began to occur. Flickering lights in the night sky and half-glimpsed figures seen in the mountains were interpreted as portents, pointing towards the end of their race. On the plateau of Fio'taun, an alliance of mountain Tau and plains Tau laid siege to the greatest fortress-city of the builder Tau. The siege had lasted five seasons, but supplies had began to run low, disease ran rampant within the city, and the plains Tau would accept no other resolution than victory through conflict.
One night, a Tau of unusual appearance entered the attacker's camp and asked to see the army's commander. Despite being softly spoken, the sentries found themselves unable to resist the stranger, and escorted him to their leader. At the same time, another mysterious Tau presented himself to those guarding the walls of Fio'taun, asking to speak to the castellan. Again, this mysterious individual was obeyed, and within the hour he led the castellan and the other leaders of the fortress-city outside the gates. Outside, the party from the fortress were met by the first mysterious Tau, himself leading a group from the besiegers' camp. Commanding the two groups to sit, the pair of mysterious Tau, calling themselves Ethereals, began to explain how the talents of the different tribes could be harnessed. They spoke of a "Greater Good" that could be achieved through unification of the tribes, and by sunrise, the two forces had declared a truce. Over the next year, more of the Ethereals appeared, preaching the messages of peace and the Greater Good across the planet, and by the end of the year, the wars were over and the Tau began to flourish like never before. Having saved their race from extinction, the Ethereals were revered with the utmost devotion by the other Tau, who readily adapted to the new caste system established by the Ethereals.
The Tau Empire rapidly developed over the next thousand years, both scientifically and in size. Within a short period of time, the Tau developed rocket technology and quickly established colonies on the moons of T'au. Access to space allowed them to develop larger vessels, which in turn allowed the Tau to travel to nearby planets. Air caste stellar cartographers discovered that the Tau homeworld resided in a dense cluster of stars, and a supernova could wipe out their entire race, prompting further expansion. The Tau discovered the existence of the Immaterium and warp technology from an alien space vessel found on one of the moons of T'au, but as their race had no psykers, they were unable to tap into the full potential of warp travel. They were able to develop limited faster-than-light technology by modifying their gravitic propulsion system to allow a starship to 'dive' towards the Immaterium, the resulting expulsion throwing the starship a significant distance. With this new technology, the Tau began to expand into interstellar space, claiming new systems and discovering alien species. In most cases, these species were incorporated into the Tau Empire, although some, such as the Orks, resisted.
The Tau Empire came into contact with the Imperium in the middle of the 41st millennium. A Tau colony ship entered an Imperial system, and was promptly destroyed by the Imperial Navy. When the bodies from the Tau ship were analyzed, it was discovered they were the same species the Explorator fleet had encountered 6000 years before. At the same time, Rogue Traders made contact with several outlying Tau sept worlds, and began trade between these worlds and Imperial settlements on the Eastern Fringe. It was at this stage that the Tau began to realise the enormous size of the Imperium of Man. Rather than be daunted by the presence of such a huge and powerful stellar neighbour, however, the Ethereals instead sent Water caste envoys to several outlying Imperial worlds where they managed to insert themselves into the Imperial commander's group of advisors. Such is the Water caste's diplomatic skill that multiple outlying Imperial worlds openly committed themselves to the Tau Empire and their quest for the Greater Good simultaneously. Alarmed by the rapid development of this xenos race and the threat of alien contamination, the Administratum declared war on the Tau, launching the Damocles Gulf Crusade. The Crusade advanced quickly, crushing any and all opposition. The Tau were subjected to horrific losses among their perimeter outposts due to the presence of Imperial Titans and Space Marines of the Iron Hands and White Scars chapters. This continued until the Imperial forces reached the Sept world of Dal'yth, where the Crusade ground to a stalemate that lasted for several months. With any hope of reinforcement cut off by pressure from the Tyranid Hive Fleet Behemoth's advance on Ultramar, the Imperial commanders accepted the Water caste's offers of peace, and were allowed to withdraw from Tau space.
In the final quarter of the 41st millennium, the Tau Empire has been assaulted by the remnants of Hive Fleet Kraken. The weakening of Imperial space by the need to defend the Cadian sector against Abaddon the Despoiler has also made open the way towards a new period of Tau colonial expansion. The Third Expansion has resulted in the establishment of several new colony worlds with minimal encroachment upon Imperial space.
The Greater Good also encompasses other races, and any races the Tau come into contact with are invited to integrate themselves into Tau society and place themselves under the guidance of the Ethereals. The races and groups that choose to incorporate themselves earn the benefits of mutual protection, trade, and access to the technology of the Tau.
Although accepting of other races, the Tau believe that their own way is superior to any other, and harbour extreme confidence in their manifest destiny to unite the stars. They are more likely to peaceably integrate races that show similar qualities to those promoted by the Greater Good. At the same time, the Tau are imperialists. Those that will not join the Tau Empire or Embrace the Tau'va (the greater good), are forced to do so via economic, political, or military means. The Tau believe the Tau'va is for the good of all, even those who do not recognize it.
Several of the novels published by the Black Library division of Games Workshop have provided more information and detail about the Tau psyche. The novel Kill Team (Thorpe, 2001) reveals that their number of digits has led them to use a base-8 number system and that their food is similar to that of humans, although varying in taste and colour. The protagonist of the novel, Kage, notices their intricate artwork, which is so subtle that it almost goes unnoticed by humans. Their architecture are also described as masterpieces in their own right, but no one tried to outdo another in splendor, in perfect harmony. The Tau characters in the novel also contrast with the brutish, militant humans with their calm, patient and quiet personalities. More important yet, as the protagonists of the book discovers, the Tau society and ideology is far more fragile than it appears at a first glance, with Tau officials going to great lengths to keep up the illusion of stability.
The Fire Caste are the soldiers of the Tau Empire. It is their duty to protect the other castes, and as such are the Tau most often used in the tabletop game. They have relatively larger muscles when compared to those of other castes, but most with strength less than that of an average human. They do not train for close combat, due to the fact that they see it as barbaric. When hand-to-hand combat is unavoidable, it is generally entrusted to Kroot and Vespid Auxiliaries. The Tau fire caste do, however, have more agility, stamina and endurance than the other castes.
The worlds of Vior'la and Sa'cea are predominantly made up of the fire caste.
Bork'an is well known for the number of its Earth caste.
Dal'yth is a sept made up mostly of Water caste.
Tau'n and Vash'ya are the more Air-caste oriented septs.
Aun is translated as either Ethereal or Celestial, and describes the mysterious Tau subspecies that ended the inter-tribal warfare of the Tau and established the doctrine of the Greater Good. The Ethereals are the leaders of the Tau, and appear to combine the roles of priesthood and royalty in Tau society. Ethereals resemble the Fire Caste in build, but are marked by a diamond-shaped ridge of raised bone in the centre of their foreheads. Ethereals are obeyed without question by the other castes, and the Imperium suspects that this control is the result of a latent pheromone-based power.
It is not unknown or even uncommon for Ethereals to become adopted into a caste, dedicating themselves as leading that group in particular. This has often been met with approval by the senior Aun who believe it allows more in-depth leadership of the infrastructure.
The Tau homeworld and the sept T'olku are both regarded to have the wisest ethereals.
Gue'vesa ("Human Helper") is the name the Tau give to the humans who have joined their empire. After the Damocles Gulf Crusade, many Imperial Guardsmen were stranded in Tau-controlled regions of space after being abandoned by the Imperium. O'Shovah helped them by giving these humans the option of joining the Tau Empire, an offer that most accepted.
In a Ciaphas Cain novel, there are a large number of people who can be considered Gue'vesa, as they support the Tau Empire over the Imperium, even though the world in question is still under the jurisdiction of the Imperium.
The descendants of the humans that joined the Tau Empire now maintain colonies on the edges of Tau space, and are often recruited as auxiliaries in the Tau army. The Gue'vesa are capable of producing copies of the Imperial lasgun to defend themselves, and in times of war may be armed with more advanced Tau weaponry such as pulse rifles, pulse carbines, and markerlights. These small units of humans are reviled and viewed as traitors by most members of the Imperium. As a result, in game terms, any Imperial units attacking Gue'vesa gain a bonus in close combat.
The Tau have many ways of addressing each other. To the Tau, the most important part of their name is the caste that they are born into and this forms the first portion of their identity. With the caste of a Tau established, the second portion of the name refers to their rank within society; there is no stigma attached to any rank or profession - each Tau has his or her place in society, and enjoys the respect of their peers no matter how menial the tasks that they perform. Each role is recognized as being part of the greater whole and a furtherance of the common good. With the exception of the 'Saal rank given to Tau children, there are five major levels of Tau rank, each of which has a subtly different meaning dependent on the caste to which it is suffixed. In ascending order of seniority, these ranks are as follows:
| Rank | Fire Caste | Air Caste | Water Caste | Earth Caste | Ethereal Caste |
|---|---|---|---|---|---|
| *'Saal | Cadet | ||||
| *'La | Warrior | Messenger | Bureaucrat | Worker | Prince |
| *'Ui | Veteran | Carrier | Envoy | Senior | Prelate |
| *'Vre | Hero | Pilot | Magister | Overseer | King |
| *'El | Knight | Captain | Diplomat | Engineer | Holy |
| *'O | Commander | Admiral | Ambassador | Planner | Highest |
The Tau of each sept are characterised by a number of influences, including the relative strength of the castes that inhabit the worlds of that sept, the location of the sept in proximity to the homeworld of T'au, climate of the inhabited worlds, and exposure to other races' cultures. These influences combine to affect the culture and attitudes of the Tau from that Sept. For example, the First Sphere sept of Dal'yth is characterised as a cosmopolitan society welcoming to non-Tau, based on the sept's location near several alien worlds and the large proportion of Water caste Tau in the population. In contrast, the attitude of stoicism and tenacious refusal to accept defeat that characterise the Third Sphere sept of Fi'rios is a result of the bloody battles required to take these worlds from the Orks.
Tau continuously establish new colonies and if a new world is already populated with humans, they do not exterminate them, unlike other galactic races, including humans as part of their belief in unity and peace (the Greater Good). The Tau believe in letting others believe what they want (including the worship of the Emperor of Mankind), but must be loyal to concept of Greater Good.
Tau ground warfare is carried out almost exclusively by the Fire caste, while the Air caste is responsible for aerial and space combat, and providing transport between systems. Fire caste military forces are known as Hunter Cadres, are similar in size and role to an Imperial Guard company, and are primarily made up of Tau from the same sept. Auxiliary forces are drawn from the alien races within the Tau Empire, and Hunter Cadres can include Kroot warriors, Vespid Stingwings, and Gue'vesa, among other forces.
Fire caste tactics are based on the concept of the "hunter". The two main schools of warfare are Mont'ka (killing blow), and Kauyon (patient hunter). Mont'ka focuses on the hunter running the prey to the ground; identifying a target of opportunity and attacking it swiftly at the right moment. A Hunter Cadre will often stand at readiness for days, waiting for the right opportunity to strike in a well coordinated and rehearsed plan of battle. Kauyon is the opposite; the hunter lures the prey into a trap through the use of bait (often a high ranking squad of Battlesuit-equipped warriors, or even the commander himself). The bait is exposed to the enemy, who, while moving to destroy the bait, are drawn into a position where they can be eliminated by the rest of the Cadre. The Tau prefer not to attack until all troops have been coordinated and the attack carefully planned.
The Tau prefer not to hold positions against enemy assault, and only construct bunkers to act as emergency shelters, or to use as a hidden observation post, or Run'al. If the enemy launches attacks against Tau installations and cities, the Tau will prefer to evacuate the installation, dismantle all important technology and come back later to destroy the enemy. If a city is too vital to lose it is protected primarily by the efforts of a Hunter Cadre to draw the enemy away. If this fails, the Cadre will perform attacks intended to stall the enemy while the location is evacuated, then fall back to the deserted city and use an urban warfare variant of Kauyon to defeat the enemy. In extreme circumstances, Mont'ka and Kauyon can be adapted to defend a vital location, but this type of warfare is heavily discouraged. Similarly, the Tau rarely fight in sieges or in close combat to force enemy from a territory, believing that it is preferable to simply kill the enemy at range, and then occupy the location with minimal losses. Against hardened fortifications, the Tau prefer to simply bombard the target, or, if it must be taken intact, isolate the area and cut off the defenders from any support. If a siege is forced, the Tau will conduct carefully-planned hit and run attacks designed to take out important defensive elements, such as leaders, communications, and heavy weapon emplacements, that reduce the overall strength of the defenders.
As the Tau Empire integrate more and more alien races, they use them more and more in their tactics. Often small alien squads will be used as bait in the Kauyon.
The Tau prefer long ranged combat over close combat. The Tau Fire Warrior's primary weapon is the Pulse Rifle, which is used alongside the Pulse Carbine. The Pulse Rifle fires molten plasma which is projected as a "beam" of plasma. The Pulse Carbine, also carried by Fire Warrior teams, sacrifices range for portability, but also carries an underslung Photon Grenade Launcher. Squads hit by the Pulse Carbine also risk being disabled by Photon Grenades. It should be noted that the Pulse weaponry used by the Fire caste is less effective against Space Marines. Indeed, the Tau have always had difficulty in combating Space Marines, especially in close combat as a Space Marines' strength far exceeds that of the Kroot.
When the Tau become engaged in close combat, they call on their mercenary allies, the Kroot. The Kroot are expert jungle fighters who appear deceptively slender, but have wiry physiques which are effectively stronger than the average human or low-level Ork boy. Many an enemy has fallen because they underestimated the Kroot. One common tactic of a Tau player is to use the Kroot as counterassault units. While the Tau are firing away at the enemy, the Kroot hide behind the lines of the Tau. When the enemy gets into charging range, the Kroot advance and charge the enemy position, buying the Tau extra time to continue firing, or withdraw to a safer position. It has also been known for Kroot to spearhead city fights, harassing enemy forces, and to clear jungles and forests, as well as clearing vital positions.
On a strategic level, the Tau tactics are best described as cautious and patient. They prefer to avoid wars of attrition, and will concentrate their efforts elsewhere if an enemy seems determined to hold a specific position.
According to Andy Chambers, the chief designer at the time, the Tau were intended "to be altruistic and idealistic, believing heartily in unification as the way forward." Graham McNeill was responsible for much of the background material produced for the Tau, developing what Andy Chambers described as "...their proud, quiet but determined character [developed] to the point where they actually became a rather likeable, if slightly naive addition to the cosmos." The Tau were updated in early 2006 with the release of a new Codex.
The Tau mini campaign counted all results involving Tau as one of the armies participating in a registered game as contributing to the expansion or contraction of Tau-controlled space. Over eight weeks of gaming, the Tau Empire expanded to almost 133% of its original size.
The Tau expedition's goal, to gather information about the warp, was largely successful; however, analysis of the gathered data, and the fates of those Tau who chose to remain behind, caused Earth caste scientists to believe that further research would be unfeasible. The Fourth Expansion of the Tau Empire was thus delayed in order to further consolidate the recent Third Expansion. As well as attaining the warp data, many human refugees joined the Tau Empire, new technologies were acquired, and Tau warriors gained valuable combat experience, though with great losses, personified with the loss of Commander Shadowsun's sibling, Shas’el Ty’res.