Sonic the Hedgehog 3 (ソニック・ザ・ヘッジホッグ3 Sonikku za Hejjihoggu Surī?) is a 1994 platform video game in the Sonic the Hedgehog series for the Sega Genesis. It was developed in the United States by members of Sonic Team working at Sega Technical Institute, and was published by Sega, debuting worldwide in the first half of 1994. The game is a sequel to the Sonic the Hedgehog 2 for the same system and follows on directly from the end of the game, in which Sonic defeated his enemy, Dr. Robotnik; crash-landing on a floating island, Sonic encounters new character Knuckles the Echidna, and must once more retrieve the Chaos Emeralds while also working to stop Dr. Robotnik from relaunching his ship, the Death Egg.The game is closely tied to its direct sequel Sonic & Knuckles, as the two games were originally developed as a single game until time constraints and cartridge costs forced them to be split into two interlocking parts.

Sonic the Hedgehog 3 and Sonic & Knuckles were originally to be released as one game,[4] but due to time and financial constraints, it was later split into two separate games. However, Sonic & Knuckles contained "Lock-on Technology", where the Sonic & Knuckles cartridge would be put in the Sega Genesis system, and then another game could be placed onto the top of the Sonic & Knuckles cartridge itself.[4] When Sonic 3 is used in this manner, it enables the player to play through both games as one, titled in-game as Sonic 3 & Knuckles. This features several additions to the games not available otherwise, such as small alterations to the levels, and being able to play through Sonic 3 levels as Knuckles, or Sonic & Knuckles levels as Tails, and the ability to save progress in all of the game's levels.Additionally, this was the only way to collect Super Emeralds, which are earned by accessing Special Stages in the Sonic & Knuckles levels after collecting all seven Chaos Emeralds from Sonic 3. When all Super Emeralds have been collected, Sonic, Knuckles and Tails can transform into Hyper Sonic, Hyper Knuckles and Super Tails respectively, each with unique abilities.