Each sept of the Tau Empire has its unique cultural identity wholly integrated within the greater Tau culture. This cultural identity seems to mainly derive from which Tau caste is more numerous and influential in the given sept. Currently there are over twenty fully developed septs. Each sept has its own sept symbol.
- T'au, homeworld of the Tau. Capital and spiritual, political, cultural, and administrative centre of the Tau empire. Its citizens are considered especially learned and wise.
- Isla'su, homeworld of the Greet.
- Pech, homeworld of the Kroot.
- Sha'galudd, homeworld of the Nagi.
- Vespid, homeworld of the Vespid.
First Phase Expansion
The Tau homeworld and the First phase colonies are of major importance and form the hub of the empire.
- T'au'n, first offworld colony, Tau from this world are considered to be pioneers.
- D'yanoi, having been isolated for a time from the empire, its inhabitants are considered somewhat rustic and backwards.
- Bork'an, centre of learning and academia.
- Dal'yth, cosmopolitan and trader-friendly.
- Fal'shia, centre of technological development, Tau from here are considered great problem solvers.
- Vior'la, a major military centre of the empire, its Fire warriors are considered especially aggressive and skilled.
- Sa'cea, another military centre, this sept has a very high proportion of very disciplined and honourable Fire Warriors.
Second Phase Expansion
- Au'taal, a beautiful sept, whose citizens are considered easygoing and often lazy.
- N'dras was abandoned for unclear reasons. Its remaining inhabitants are regarded as unstrustworthy, quick-tempered, and of brooding countance.
- Ke'lshan has suffered several raids by several alien races. Tau from this sept have grown mistrustful, solemn, taciturn, unfriendly and sometimes openly hostile to alien races. Ke'lshan was invaded by Hive Fleet Gorgon and played an essential role in stopping it.
- Elsy'eir is known for its poetry and artwork. Its citizens are considered intellectuals and well-respected for their creativeness.
- Tash'var was raided several times by Orks and pirates. Its people are regarded as tenacious, hardy, practical and courageous.
- Vash'ya seems to be primarly inhabited by members of the Air caste.
- T'olku is known for the skill of its Ethereal diplomats.
Third Phase Expansion
The Third Phase Expansion was convened on 977.997.M41 on the word of Aun'va. Commander Shadowsun was placed in command, and secured at three new septs for the Tau Empire. During the Zeist Campaign of 999.M41, Space Marines forces counterattacked against the expanding Third Sphere, drawing the Third Sphere to a, perhaps temporary, halt. The three septs formed from the Third Sphere Expansion are:
- Ksi'm'yen's colonists seem to be associated with luck, subtlety and opportunistic subterfuge.
- Fi'rios whose pioneers are recognised for a tenacious refusal to accept defeat, tempered by a stoic acceptance of the price all must pay in the furtherance of the Greater Good.
- Mu'gulath Bay, previously known as the Imperial Hive World of Agrellan. (Destroyed)
Fifth Phase Expansions
After the ill-fated Fourth Sphere of Expansion reestablished contact with the Tau Empire after decades of being thought lost a new campaign was immediately launched through a wormhole known as the Startide Nexus. Rapidly, worlds on the other side of the rifts have been colonized.
Known Fifth Sphere septs include:
These are Septs that are not credited to a specific phase of expansion; some have been formed individually, through opportunity or a smaller scale invasion. Some may not even be Septs, but rather a splinter of another Sept.
- Vas'talos, previously known as the Imperial Fortress World of Prefectia.
- Shans'et — formerly the Imperial world of Gossamehr
- Gates of Petros
Besides the populous septs, there are also sparsely populated colonies. Only a few names are known.
- Es'Tau, settled during the Second Expansion.
- T'ros, settled during the Third Expansion.
- Sha'draig — invaded by Hive Fleet Gorgon in 900.M41. Gorgon was eventually driven off the world, but not before it was almost completely consumed by Ripper swarms.
- Ka'mais — invaded by Hive Fleet Gorgon in 902.M41. A hidden Necron fleet emerged from Ka'kais' dead moon and destroyed the outnumbered Tyranid ships, but then continued to land on Ka'mais and harvest the planet.
- Ho'sarn — was evacuated in 902.M41 as Hive Fleet Gorgon approached. But the evacuation fleet was ambushed by the Hive Fleet and completely slaughtered.
- Kor'var — Site of the destructive ongoing Kor'var Campaign
- Ky'san — Site of a Kroot uprising
- Va'yun — Raided by Eldar Corsairs
- Shi'yen — Colony for client races
During the First phase expansion the homeworlds and colonies of the Kroot and of the Vespid were also incoporated into the Tau empire. Notice that these star systems are not considered septs. In addition there an unknown number of former Imperial worlds in the Tau Empire, such as T'ros. Some or all of which might still have a Human population.
- Pech, homeworld of the Kroot. According to the maps there are eight star systems inhabited by the Kroot (including Pech). We know the name of only one, Krath, where the Tau first encountered the Kroot.
- Caroch, Kroot world
- Akchan-Kur, Kroot world
- Vespid, homeworld of the Vespid.
- Isla'su, homeworld of the Greet
- Sha'galudd, homeworld of the Nagi
- Roksh XVI — site of a secret Tau listening post, the planet was part of the Roksh system that was home to the Rokshashi Wealthweb merchant guild before the entire system was consumed by Gorgon in 689902.M41.
- Yuun'chen, Kroot world
Three Artefact worlds are located within the borders of the Tau empire. As the name indicates, ancient artefacts of unknown origin have been discovered there. It is not known if these worlds have Tau colonies at all.
- Arthas Moloch, a dead world where Commander Farsight found the Dawn Blade.
- Landfall[Needs Citation]
- 1: Codex: Tau Empire (4th Edition), pg. 42
- 2: Warhammer 40,000 5th Edition Rulebook, pg. 129
- 3: Codex: Space Marines (5th Edition), pg. 48
- 4: Kill Team (Novel) by Gavin Thorpe, [Needs Citation], pg. 137
- 5: Imperial Armour Volume Three - The Taros Campaign, [Needs Citation]
- 6: Codex: Tyranids (5th Edition), pgs. 18–21
- 7: Codex: Tau Empire (8th Edition) pg.80
- 8: Voice of Experience (Short Story)
- 9: Codex: Drukhari (9th Edition) pgs. 39-42