Euphoria is a game animation middleware created by NaturalMotion based on Dynamic Motion Synthesis, NaturalMotion's proprietary technology for animating 3D characters on-the-fly "based on a full simulation of the 3D character, including body, muscles and motor nervous system".

[1] Instead of using predefined animations, the characters' actions and reactions are synthesized in real-time; they are different every time, even when replaying the same scene.

A press release that was enclosed with the second trailer eventually confirmed that Grand Theft Auto IV is the first of Rockstar's games to feature Euphoria.

The Star Wars titles, Star Wars: The Force Unleashed and The Force Unleashed II use Euphoria, as do games based on the Rockstar Advanced Game Engine (RAGE) including Grand Theft Auto V and Red Dead Redemption 2.

[6] In 2017, NaturalMotion announced it would end licensing of Euphoria, along with its other technologies, to concentrate on mobile games.