From the back of the book:
For hundreds of years the Horrors ravaged the world unchecked.
Only magical traditions passed down from generation to generation enabled us to face these evil entities with any hope of victory. Our knowledge of the Disciplines has grown with the passing of years, and now we can infuse our swords and spells with powers we once only dreamed of. But others, too, have grown stronger...
The Earthdawn Companion provides rules for advancing characters far beyond the limits set in the Earthdawn rulebook: expanding the existing Disciplines to Fifteenth Circle; offering new talents and spells; and providing rules for expanding characters' use of thread magic. The Companion also supplies rules for playing questors and Lightbearers, rules for ship combat, and guidelines for creating new disciplines and creatures.
An Earthdawn supplement for gamemasters and players.