Sonic the Hedgehog 2 (ソニックザヘッジホッグ2, Sonikku za Hejjihoggu 2) is an 8-bit 1992 side-scrolling platform video game developed by Aspect Co., Ltd. and released by Sega for their Master System and Game Gear formats. The Master System version was released in Europe on October 16, 1992, and in Brazil around the same time. The Game Gear version was release in Europe on October 29, 1992, North America on November 17, 1992 and in Japan on November 21, 1992.

Being released before the 16-bit version for the Mega Drive (Genesis), the 8-bit editions of Sonic the Hedgehog 2 represented the debut of character Miles "Tails" Prower, who became a recurring character in the series.

The Master System version was released for the Nintendo Wii's Virtual Console on November 18, 2008 in Japan, in North America on December 8, 2008 and in the PAL regions on December 26, 2008.

Advances made in this game include Sonic's ability to grab back rings scattered when hit by an enemy as well as being able to smash through certain walls, capabilities not implemented in the 8-bit versions of the original title. There is no Spin Dash because this game was released before the Mega Drive version, which introduced the Spin Dash. Uniquely, this game includes levels in which Sonic must ride a mine cart, and a hang glider, the latter under full player control and a reasonable simulation of physics. There is also a large bubble in underwater levels which raises Sonic upwards until he hits a ceiling, enemy or obstacle. Sonic is also able to skim at high speed across the surface of water.

There are seven zones in total, each comprising three acts. In the final act, that level's boss is faced, but without any rings to collect (hence Sonic cannot survive taking any damage in these battles). Rather than facing Robotnik himself (with the exception of the final stage and some involvement in the first boss), Sonic faces up against a bunch of robotic animals: a giant antlion, a mother ostrich and many of her robotic chicks, a circus sealion, a sumo pig (some believe it to be a bull), and a spiky-backed boar. At the end of the sixth stage, Sonic encounters a robotic doppelganger of himself (dubbed "The Silver Sonic"), the first such robotic "Sonic" of the series. At the end of Acts 1 and 2 of each level, a panel is spun, with a reward given based on what it lands on.

Item boxes are largely the same as the first game (although the restart marker and shield devices have been removed), and like the previous game, Chaos Emeralds are scattered throughout the stages. One is found in the second act in each of the first five zones. If the player collects these five and then destroys Mecha Sonic in the third act of the sixth zone, the sixth emerald is relinquished and the player may access the final stage (Crystal Egg), in the third act of which Doctor Robotnik is faced in a final boss battle. Players able to complete the full task are rewarded with the game's "good ending" which involves Sonic and Tails running along before looking to the sky to see themselves amongst the stars at night. For those who fail to collect all five of the hidden emeralds, play ends after Mecha Sonic's destruction and, with a more downbeat end sequence, Sonic runs alone before looking up at the stars to see Tails alone. This may mean that Dr. Robotnik has killed Tails. This ending also plays if players complete the final stage having accessed it through a level select cheat.