Sonic the Hedgehog 3 is a 1994 platform game developed and published by Sega. It is part of the Sonic the Hedgehog series and the sequel to Sonic the Hedgehog 2 (1992). Following the events of Sonic 2, Doctor Robotnik's spaceship, the Death Egg, crash-lands on a mysterious floating island. There, Sonic and Tails must once more retrieve the Chaos Emeralds to stop Death Egg from relaunching, while making rounds with the island's guardian, Knuckles the Echidna. Gameplay is similar to previous entries, with players controlling Sonic and Tails through side-scrolling levels at high speeds while collecting rings and defeating enemies.

Development began in January 1993, shortly after the release of Sonic 2. It was initially developed as an isometric game similar to Sonic 3D Blast (1996), but became a more conventional 2D platformer due to time constraints. Sonic 3's production took place simultaneously with Sonic & Knuckles; they were developed as a single game until time constraints and cartridge costs forced the developers to split them in two projects. The Sonic & Knuckles cartridge features "lock-on" technology that allows it to be physically attached to the Sonic 3 cartridge, creating a combined game, Sonic 3 & Knuckles. Pop musician Michael Jackson reportedly composed portions of the soundtrack, but left the project and went uncredited.

Sonic 3 was released for the Sega Genesis in North America and Europe in February 1994, and in Japan the following May. As with its predecessors, it was a critical and commercial success, with critics seeing it as an improvement over previous installments. It sold over one million copies in the United States, making it one of the bestselling Genesis games. Sonic 3 has been rereleased in compilations and download releases for various platforms, including Sonic Mega Collection for the GameCube and Sonic's Ultimate Genesis Collection for the PlayStation 3 and Xbox 360.