Sonic Adventure is the first Sonic game to be released for the Sega Dreamcast and was also a launch title at the time of the Dreamcast going on sale. The game also saw a revamp to the designs of the Sonic series characters and Dr. Robotnik was now referred to as Dr. Eggman outside of Japan.
 Sonic Adventure DX
The game was later re-released on Gamecube and PC as a special extended edition known as Sonic Adventure DX Director's Cut. This edition featured improved graphics, more emblems, an enhanced Chao raising system and the ability to unlock 7 Game Gear games. Additionally the Gamecube version could be connected to Sonic Advance and Sonic Advance 2 to import Chao data.
The original game was ported and enhanced on the Gamecube and PC. Additionally the original game was ported to Xbox Live and Playstation Network as Sonic Adventure, which could then be upgraded to the DX edition with an extra DLC pack. The XBLA and PSN versions of Sonic Adventure DX did not include the unlockable Game Gear games or, obviously, the Gameboy Advance connectivity.
The game was also included on the Dreamcast Collection compilation.
The game introduces several new characters such as Big the Cat, Tikal and E-102 Gamma. Also introduced for the first time was the Chao, small creatures that act somewhat like a virtual pet that can be raised in-game.
 Playable Characters
The game has six playable characters, each with their own storyline which branches off and crosses over with the other characters in the game.
- Sonic The Hedgehog - His adventure begins when he is relaxing in Station Square and notices the police fighting a water creature named Chaos. When Sonic realizes that Eggman is the mastermind behind Chaos, he must find out the mysteries behind Chaos and stop Eggman from getting all 7 Chaos Emeralds.
- Miles "Tails" Prower - His adventure begins when he crash lands on the beach and is saved by Sonic. Now he is helping Sonic on his quest to stop Eggman and get the Emeralds.
- Knuckles the Echidna - His adventure begins when when Chaos appears on Angel Island, breaks the Master Emerald, and causes the island to fall into the ocean. Now Knuckles must find all the Emerald pieces and get Angel Island back into the air.
- Amy Rose - Her adventure begins when a bird falls from the sky and lands on her head. Then a robot name Zero drops out of Eggman's ship, the Egg Carrier, and tries to get the bird back from Amy. After Amy and the Bird escape from Zero, Amy promises that she will protect the bird at all costs.
- Big the Cat - A new character to the series, he is a big, fat, lazy purple cat who enjoys fishing with his friend, Froggy. His adventure begins when he and Froggy are sleeping and something shakes the whole forest. When Froggy wakes up to see what it was, he finds Chaos. After accidentally swallowing some of Chaos, Froggy grows a tail and get possessed by Chaos. When Big wakes up, Froggy swallows his Chaos Emerald and runs off. Now Big must catch Froggy and find out why he's acting so weird.
- E-102 Gamma - A robot created by Eggman as one of the E-100 series. After Amy explains to him that Eggman is evil, he realizes that he must stop taking orders from him and that he must "rescue" the other E-100 machines.
- Metal Sonic - Metal Sonic is a special character only featuring in the DX edition of the games, and is unlocked once all of the games emblems have been collected.
 Non-Playable Characters
 Action Stages
- Emerald Coast
- Windy Valley
- Ice Cap
- Sky Chase
- Twinkle Park
- Speed Highway
- Red Mountain
- Sky Deck
- Lost World
- Final Egg
- Hot Shelter
- Sand Hill
 Adventure Fields
- Egg Hornet
- Egg Walker
- Egg Viper
- E-101 Beta
- E-103 Delta
- E-104 Epsilon
- E-105 Zeta
- Chaos / Perfect Chaos
Music from the game features in the following CD soundtracks: