From the Back of the Book:
Within the Ethereal Plane, demiplane islands and creatures both odd and dangerous float in an endless field of possibility. Canny folks know that the Ethereal also leads the way to the Inner Planes, infinite arenas of elemental fury. See, it's more than just a backdrop to other adventures - the plane itself offers wonder and opportunity for those with courage enough to explore its limitless expanse. This guide includes the following information:
- Ethereal environments and conditions - including methods of getting there in the first place.
- How the alien medium of the Waveless Sea affects combat and magic.
- New spells, magical items, and proficiencies dealing specifically with the Ethereal Plane.
- The chant on demiplanes - islands in the Deep Ethereal that obey no rules but their own - including information on old and new demiplanes, plus DM guidelines for creating these unique "pocket dimensions."
- A complete listing of the creatures of the Ethereal, including several new monsters and an Ethereal Encounter Table.
- Two new Ethereal-based player character races: nathri and renegade nethlings.