From the publisher's website description:
Explore a savage, wondrous world.
Aimed at players and Dungeon Masters, this game supplement explores the heroes and wonders of Athas - a savage desert world abandoned by the gods and ruled by terrible sorcerer-kings. Use it to build Dark Sun heroes and thrilling D&D adventures set in the Seven Cities of the Tyr Region, the Ivory Triangle, the Sea of Silt, and monster-infested wastelands - or plunder it for your own D&D campaign!
The Dark Sun Campaign Setting provides exciting character options for D&D players, including new races, new character themes and class builds, new paragon paths and epic destinies, and new equipment. It also provides everything Dungeon Masters need to run 4th Edition Dark Sun campaigns or include Dark Sun elements in their homebrew campaigns. It has rules and advice for handling survival challenges, arena encounters, desert terrain, and adventure creation. It also presents a short, ready-to-play introductory adventure.