From the back of the book:
Command the Elements
Imagine untamed oceans wracked by lightning, whirlwinds of seething flame and roaring thunder, and massive shards of flying earth and ice. Welcome to the Elemental Chaos, the raw plane from which the gods and the primordials fashioned the world. The plane forms the foundation of the D&D cosmos and is home to countless elemental beings, including genies, archons, and demons. It's also a source of tremendous arcane power, the place where all fireballs and lightning bolts are born.
Now you can play a hero who harnesses the raw power of the Elemental Chaos. Player's Option: Heroes of the Elemental Chaos presents the elementalist sorcerer and the sha'ir wizard as new class options, as well as new character themes, feats, powers, paragon paths, epic destinies, and elemental companions.