The Tau '''caste system''' divides all [[Tau]] into 5 groups known as '''castes'''. The castes are named after the elements of nature, and closest to the particular caste in question. Movement between the castes seems to be impossible, and membership One's caste is determined at birth and inherited by one's parents. Inter-breeding is forbidden by the Etherals. To choose another caste for himself seems to be impossible, and held contrary to the notions of the [[Greater Good]]. The castes are based upon the racial and political divisions that separated the Tau on their [[homeworld]] of [[T'au ]] during the time of the [[Mont'au]].

Members of the Fire caste are the warriors of the [[Tau Empire]], and as such are most often seen on the field of battle. They are taller and stronger than the members of the other castes, although still weaker and shorter than the average human. These traits come from the Fire Caste's origin on the plains of [[T'au]], the Tau home world, where they were hunters and warriors. Tau from the world of [[Vior'la]] tend to have slightly even greater muscle mass than the norm because of the increased gravitational pull stronger gravity of the that planet.

This caste provides for the manufacturing, agricultural, industrial, and engineering needs of the Tau Empire, including being the builders, farmers, scientists, and engineers, etc. They are often described as plain and dour, possessing a rather stoic outlook on life in general. They were originally the first Tau to build cities and practice agriculture. The city of [[Fio'taun]] is an example of this, being the first place where the Ethereals appeared.

The Air Caste is charged with holding the Tau Empire together through the [[Kor'vattra]], the Tau Empire's merchant and warfleet. They function not only Formerly functioning as messengers, but these days they are also the Tau Navy. The Tau of the Air Caste are the tallest and most slender of all Tau, with long, skinny limbs and hollow bones developed due to lives lived mostly in low- and zero-gravity ships and space stations. In the past, before the time of the Mont'au, the Tau that originally became the Air Caste had membranes stretching between their limbs, allowing them to glide on air currents. Tau pilots tend to be superior pilots compared to humans their human counterparts because they have a better depth perception and higher G-tolerance, but lack battle-experience compared to the best Imperial fighter-pilots.

The Water Caste serve the Tau Empire as traders, merchants, public servants, diplomats, and ambassadors. They interact with other races when such affairs are not handled by the Fire Caste. The Water Caste tend to be tall and slender compared to other Tau.

The [[Ethereal|Ethereals]], these mysterious Tau, s serve as "philosopher kings" , and guide the other castes , as well as Tau Empire alien member-races of the Tau empire, towards the enlightenment of the ''Tau'va''; the [[Greater Good]].