Phantasy Star III: Generations of Doom, released in Japan as Toki no Keishōsha: Phantasy Star III (時の継承者 ファンタシースターIII^?), is a traditional console role-playing game that was released for the Sega Mega Drive (Sega Genesis) in Japan in April 1990 and in western countries in 1991. It was also released in three different compilations known as The Phantasy Star Collection for the Sega Saturn and Game Boy Advance, and The Sega Genesis Collection for the PlayStation 2 and PSP, and later re-released on the Virtual Console. It was featured in Sonic's Ultimate Genesis Collection for the Xbox 360 and PlayStation 3.

Phantasy Star III is a sequel to the previous game in the series, Phantasy Star II, although the connections to other games in the Phantasy Star series are not immediately evident. Gameplay is similar to the games before it in the series, with combat still being turn-based and battles randomly occurring. Players must explore both overworld maps and dungeons in order to progress through the game.