| Sonic the Hedgehog 3 came out in North America on 2 February 1994 and in the UK on 24 February; some European countries and Australia followed in March, and Japan on 27 May. | "Happy blue year" section | Interview |
| Sega advertised Sonic & Knuckles as "playing worldwide" on the Genesis from 18 October 1994, and a Tokyo shop's advertisement in Beep! MegaDrive lists it in Japan for 18 October. | "New shoes" section | Magazine |
| In Sonic 3, Knuckles is an antagonist who knows the island's hidden passages and blocks Sonic's path. Takashi Iizuka said the plan from the start was that Knuckles would first be an enemy and later become playable. | Iizuka on Knuckles in the story | Manual |
| Retro Gamer credits Knuckles's design to Takashi Yuda. | on the new playable character | Interview |
| Takashi Iizuka said Knuckles's punch through rock let the team build routes only he could use, and his climbing and gliding brought vertical play to stages built for Sonic's horizontal one. | Iizuka on Knuckles's abilities | Interview |
| Takashi Iizuka gave Retro Gamer a different reason for dropping the SVP chip: the work was a research experiment in moving Sonic in 3D, and since the chip handled only about as many polygons as Virtua Racing, the team judged it not a good fit for a Sonic game. | on the SVP chip and the deadline | Interview |
| Takashi Iizuka said the team wanted more stages, each several times larger than Sonic 2's, but it had a date to meet and the cartridge couldn't hold the whole game; of the promotion that set the date, he told Retro Gamer "it wasn't realistic to change that". He said splitting it would have left the Knuckles routes built into Sonic 3's stages unplayable, since two cartridges couldn't share data, and that this led to the lock-on cartridge. | on the SVP chip and the deadlineIizuka on the split | Web |
| Retro Gamer reports that the split moved Flying Battery Zone, planned between Carnival Night and IceCap, to become Sonic & Knuckles's second zone. | on the split's effects | Interview |
| Takashi Iizuka said he didn't think the split added or moved other stages, but it changed some: Launch Base, now Sonic 3's last zone, got an extra boss, Big Arms, and Mushroom Hill, now Sonic & Knuckles's first, was made easier than planned. | Iizuka on the split's effectsIizuka on the split's effects | Interview |
| Sonic 3 was made at Sega Technical Institute in the United States by an almost wholly Japanese staff, while the institute's American developers moved to Sonic Spinball; Sega-16's history of the institute says the Japanese unit made both Sonic 3 and Sonic & Knuckles. | on the team | Interview |
| Mean Machines Sega scored Sonic & Knuckles 85%. Gus found its likeness to Sonic 3 "almost disturbing", and Steve Merrett judged it "every bit as good as Sonic 3" but "more of the same"; the box praised the lock-on for putting life into games already bought. | "New shoes" section | Magazine |
| Retro Gamer reports that Sonic 3 and Sonic & Knuckles together sold four million copies. | "New shoes" section | Interview |
| Sonic 3 and Sonic & Knuckles came to the PC in 1997 as Sonic & Knuckles Collection, playable apart or together, with MIDI music that replaced some tracks. They came to the Saturn in Sonic Jam the same year, and emulated versions were part of Sega's compilations until 2010. | "New shoes" section | Interview |
| Sonic Origins (2022) brought back Sonic 3 & Knuckles as one game, Retro Gamer reports, and VGC reports Sega saying in a livestream that it couldn't use "all the original sounds" of the Genesis game and that Jun Senoue had adapted the music composed in 1993. | closing section | Interview |
| Takashi Iizuka said he had wished to sell Sonic 3 and Sonic & Knuckles as one complete game, and was happy that Sonic Origins did. | Iizuka, closing section | Interview |
| Retro Gamer's feature on Sonic 3, republished online in 2024, says Sonic fans tend to hold Sonic 3 & Knuckles the best of the classic games. Jeremy Parish's 2013 USgamer list of the best Genesis games put Sonic & Knuckles eighth, counting votes for Sonic 3 & Knuckles with it, and Eurogamer's Dan Whitehead wrote in 2009 that Sonic 3's stages "now sprawl in many directions". | closing section | Interview |