Thieves' World is an RPG setting based on Robert Asprin's and Lynn Abbey's short story anthologies "Thieves' World".
In 1981 Chaosium published a well regarded boxed set, based on the first two books of the anthologies, which was notable for supporting many of the RPG systems extant and popular at the time. During 1982 FASA published three licensed universal adventures and a promotional mini-module handed out at conventions. In 1986 Chaosium published a setting supplement, Thieves' World Companion, that covered books 3-6 of the anthology series.
Chaosium's publications are grouped into Chaosium Thieves' World.
In 2005 a d20 system Thieves' World RPG was published by Green Ronin for the same setting.