Straight from GW itself.
As one of the most technologically advanced races in the Warhammer 40,000 universe, it was only a matter of time before their Codex was released as an eBook as part of our ever-expanding range of Digital Products. As an eBook Edition it is fully compatible with Android, Kindle and iBook devices, which means that no matter what form of technological wizardry you prefer, you can download Codex: Tau Empire for it. As with all our eBook Editions, it contains all the great content of the physical Codex, including background sections, artwork, a full army list and a miniatures showcase.