The T'au Empire (pronounced "TOW" as in "WOW"), also spelled Tau Empire in older Imperial records, is a rapidly expanding, multispecies xenos stellar empire situated within the Imperium of Man's Ultima Segmentum, near the Eastern Fringes of the Milky Way Galaxy. It lies within the reach of the Astronomican.

The T'au Empire was founded by the T'au caste called the Ethereals, who lead the T'au Empire in the name of and in accordance with the utilitarian philosophy they have named the "Greater Good" (Tau'va in the T'au Lexicon). A large and growing number of other intelligent, alien races have allied themselves with the T'au within the empire.