The Third Age is the name of a “meta-series” — as in, an overarching series of books that contains other series within it. Think “Pern” or “Darkover”.

These are all the series within The Third Age at present, followed by a recommended reading order.

The Bellica Trilogy

Bellica
The Jade Star of Athering
Anala

The Isis Duet

Isis Awakening
Isis Ascending