Sonic Riders: Zero Gravity is a hoverboard racing video game developed by Sonic Team and published by Sega for the PlayStation 2 and Wii. It is the fifth racing game in the Sonic the Hedgehog series, and the second entry the Sonic Riders trilogy. A port for the Xbox 360 was cancelled during development, while a sequel, Sonic Free Riders, was released exclusively for that system in 2010.

Gameplay in Zero Gravity is largely similar to its predecessor, with characters racing on different types of hovercraft called "Extreme Gear". In addition to the mechanics from the previous game, Zero Gravity adds a new gameplay system based around gravity that replaces the predecessor's "fuel" system. During the race, performing tricks and other actions will increase a character's Gravity Points, or GP. If players have accrued enough GP by the time they enter certain areas of the track, they will enter a Zero-Gravity Zone, where they can perform one of two maneuvers. A Gravity Dive will create a small black hole that points gravity forward down the track, giving the player a powerful free-fall boost that is further augmented by striking objects in the vicinity that the hole displaces, such as cars or signs. Alternatively, Gravity Control will alter the gravity of the course, allowing players to reach otherwise-inaccessible areas and shortcuts. Players can also use Gravity Drift to more easily maneuver around sharp corners.

The Babylon Rogues retrieve an Ark of the Cosmos, one of five relics capable of controlling gravity, intending to use them all to power Babylon Garden's warp engine. Other Arks fall from the sky, with one of them striking technology company MeteoTech's Crimson Tower. As a result, the robots inside go haywire and begin a global rampage. Sonic, who is traveling with Tails and Knuckles, finds one of the Arks. He is attacked by the robots, but uses the Ark's power to escape. While being pursued, the trio runs into Amy, who has also found one of the Arks. The four head to MeteoTech to investigate, where they run into the Rogues, and Storm chases after Amy in an attempt to take her Ark. The others venture further inside, where they discover the company's owner, Doctor Eggman. Eggman reveals that one of the robots, SCR-HD, was struck by the Ark that hit Crimson Tower, giving it sentience and leadership over the other robots. The robots now seek to obtain all five Arks, one of which Eggman used to power the mother computer which controls all of MeteoTech.