The race was ruled by a caste of psykers. The Shishell had five castes: Earth, Air, Fire, Water, and Spirit. Like the Lizardmen, the Shishell had a caste-based society. Initially, he conceived them as the counterpart to the Lizardmen faction from Warhammer Fantasy, in the same way the Eldar are the counterpart of the High Elves, and he called them 'the Shishell'. Gavin Thorpe began developing what eventually became the Tau in the early 1990s.

Kroot warriors provide melee support, while the insectoid Vespids serve as jump infantry. The Tau are the only army in the game that routinely incorporates aliens from other species. AI drones act in a support role, offering fire support, specialized equipment, laser guidance, or physical protection for manned units. The bulk of their heavier units are made up of battlesuits which act as mobile heavy weapons platforms piloted by single soldiers. Most T'au vehicles have the 'Fly' keyword, allowing them to move over terrain without issue. There are, however, optional rules in the Open Play format for including psyker auxiliaries from other races as well as Relics for use in Narrative Play that allow models to counter psychic powers. The T'au do not have any psykers nor units that specialize in countering psykers, which makes them somewhat more vulnerable to psychic attacks. While most armies in 40k may only make a single overwatch action a turn, Tau have no such limitation, and may even have units fire overwatch for close by allies. They heavily use the Overwatch special rule, which allows them to shoot back at their enemies when charged, with devastating power. They have some of the most powerful ranged weaponry in the game in terms of both range and stopping power. The T'au specialized in ranged warfare and die quickly in melee. Warhammer 40,000 game mechanics (as of 9th Edition) 2.2 Influence of the Eye of Terror campaign.1 Warhammer 40,000 game mechanics (as of 9th Edition).

Tau warhammer