They are humanoid in shape, but they aren't very human-like, being more akin to the "green men" of pop culture. They have three distinctive chastes between the race, that belong to the same hatches and parents. The chastes aren't as easy to define in human terms, as the "obvious" leaders, the so-called mandarins, aren't actually the leaders but the leadership is divided among the three chastes depending on the world.
If the Vau were to expand into Human Space, no one is sure if they could be halted, for their tech is impressive. Human’s stole their own knowledge about energy shields and blasters from early Vau encounters. It is theorized that the Vau know far more about these fields than has been revealed.
Humans aren't allowed to enter on Vau space except from a few worlds. All diplomatic contact is made at an island in Vril-Ya, but they are insofar frustrating enough to be a dead destiny. The main efforts are made by House Justinian.