Undertale (also stylized as UNDERTALE) is a role-playing video game developed and published by indie developer Toby Fox. The game was released for Microsoft Windows and OS X on September 15, 2015.

Players control a human child who has climbed a mountain and fallen into the Underground, a large, secluded region underneath the surface of the Earth separated by a magic barrier. The human interacts with many monsters while on a quest to return to the surface, with the player making decisions on whether to kill or befriend them. Some of these decisions are made through the game's turn-based combat system, in which the player, after navigating through mini-bullet hell segments, can opt to talk or spare monsters instead of attacking and killing them. The choices made by the player affect the outcome of the game, with the dialogue and story outcome changing based on their decisions.