Sonic Adventure (ソニックアドベンチャー, Sonikku Adobenchā?) is a platform video game developed by Sonic Team and published by Sega. The sixth installment in the Sonic the Hedgehog series, it was first released in Japan in 1998 as one of five launch titles for the Dreamcast. The final updated edition, titled Sonic Adventure International, was released as a launch title on September 9, 1999, in North America and on October 14, 1999, in Europe. It has sold over 2.5 million copies, making it the best-selling Dreamcast game.
An enhanced port was released in 2003 as Sonic Adventure DX: Director's Cut for the Nintendo GameCube and in 2004 for Microsoft Windows. The game was ported to Xbox Live Arcade on September 15, 2010 and PlayStation Network on September 20, 2010. The game was featured on Dreamcast Collection, a four-game bundle released for Xbox 360 in 2011.
A sequel entitled Sonic Adventure 2 was released in 2001.