Thessia is the Asari homeworld, roughly the size of Earth, and home to 5.5 billion Asari. It is located in the Athena Nebula.

Shepard visits Thessia on the advice of the Asari Councillor, in an attempt to find the Catalyst which can complete the Crucible and destroy the Reapers. Instead, he locates a Prothean Virtual Intelligence which gives him further advice.