Sonic & Knuckles is the fourth video game in the "Sonic the Hedgehog" series. It was made by Sonic Team and published by Sega for the Sega Mega Drive in 1994. In the game, you are able to play as Sonic the Hedgehog and Knuckles the Echidna. You can insert a "Sonic the Hedgehog 2" or "Sonic the Hedgehog 3" cartridge into it and you will get new modes for those games. This is called "Lock-on Technology".