Sonic & Knuckles is a 1994 platform game developed and published by Sega. Players control Sonic the Hedgehog and Knuckles the Echidna in their quests to save Angel Island; Sonic tries to prevent Doctor Robotnik from relaunching his orbital weapon, the Death Egg, while Knuckles scuffles with Robotnik's minion, EggRobo. Like previous Sonic games, players traverse side-scrolling levels at high speeds while collecting rings and defeating enemies.

Sega Technical Institute developed Sonic & Knuckles simultaneously alongside its predecessor, Sonic the Hedgehog 3 (1994); they were planned as a single game until time constraints and cartridge costs forced the developers to split it. The Sonic & Knuckles cartridge features an adapter that allows players to connect the Sonic the Hedgehog 3 cartridge, creating a combined game, Sonic 3 & Knuckles. Sonic the Hedgehog 2 (1992) can also be attached, allowing players to control Knuckles in Sonic 2 stages. Attaching the original Sonic the Hedgehog or any other Genesis game released prior to this will unlock the "Blue Sphere" minigame.

Sonic & Knuckles was released for the Sega Genesis on October 18, 1994. It received positive reviews; critics were impressed with the replay value and lock-on technology, despite its similarity to Sonic 3. The games sold a combined four million copies worldwide, placing them among the best-selling Sega Genesis games. They have since been rereleased in various Sega and Sonic compilations.