Sonic Adventure is a 3D platformer video game in the Sonic the Hedgehog series. The player can control six characters from the Sonic universe, each with their own gameplay and point of view of the story. The game is divided up into two types of levels: Action Stages and Adventure Fields. The division of Action Stages and Adventure Fields are a serious departure from all previous Sonic games. Adventure Fields are non-linear game stages that contain very few items, generally designed for puzzle solving, exploration and plot advancement. Action Stages are more speed based and have Rings scattered in them. Sonic Adventure was the top-selling Dreamcast game and received a sequel in 2001, marking the 10th anniversary of the Sonic the Hedgehog series.

Doctor Robotnik seeks a new way to defeat his longtime nemesis Sonic and conquer the world. During his research he learns about an entity called Chaos, a creature that helped to protect the Chao and the all-powerful Master Emerald thousands of years ago. When a tribe of echidnas sought to steal the power of the Emeralds, breaking the harmony they had with the Chao, Chaos retaliated by using the Emeralds' power to transform into a monstrous beast, Perfect Chaos, and wipe them out. Before it could destroy the world, Tikal, a young echidna who befriended Chaos, imprisoned it in the Master Emerald along with herself. Eggman releases Chaos and Sonic and his friends must act against Eggman's plans and prevent the monster from becoming more powerful.