Dark Sun is set on Athas, once a verdant paradise, but now mostly desert. Its people escape the terrors of the creatures and plants that survive in the sands by huddling in city-states, everyone under the oppressive reign of an evil sorceror-king who wields god-like power. They fight in the gladiatorial arenas, or bet their valuables on the outcome: crystal and bone (the only workable materials; Athas has almost no metal), or most precious of all, water.
Magic is shunned and mistrusted as the power which defiled the land, while psionic powers have become commonplace. Athas has been deserted by gods, so clerics worship the elements instead. Dwarves swear oaths they never break, and sire half-cast sterile offspring with humans; feral nomadic elves run across the desert sands; cannibal halflings hide in the few patches of jungle left, far beyond the mountains; half-giants pull trader's ships through deadly seas of sand; and other, stranger races, more like insects or pterodactyls than men, watch it all.
Dark, grim and deadly, Dark Sun presents a very different alternative to the traditional high fantasy settings of Dungeons & Dragons.