Sonic the Hedgehog Chaos (also known as Sonic Chaos, known in Japan as Sonic & Tails) is a 2D side-scrolling platformer developed by Aspect and published by Sega for the Sega Master System (on October 25, 1993 in Europe only) and Sega Game Gear (in November 1993).
The third 8-bit platformer in the Sonic the Hedgehog series (after the SMS/GG versions of Sonic the Hedgehog and Sonic the Hedgehog 2), Chaos has players control either the titular hedgehog (or his furry companion Tails) as they set out to reclaim the red chaos emerald of South Island from Dr. Robotnik.
Unlike the previous two 8-bit platformers, players can perform the Spin Dash command to regain their high speed and bypass most enemies and obstacles in their way. Both Sonic and Tails have their own strengths and weaknesses: Sonic can enter special stages to earn chaos emeralds and use the "rocket boots" power-up to glide through the air for a short time, while Tails can fly and start with more lives and continues.
It is the last game in the series released for the Sega Master System outside of Brazil, and received a sequel for the Game Gear a year later. The GG version was also included as a hidden mini-game in the 2003 game Sonic Adventure DX: Director's Cut, in the 2004 compilation Sonic Mega Collection Plus, and in the 2005 compilation Sonic Gems Collection (as a limited "demo") The SMS version was digitally re-released for the Wii (via Virtual Console) on February 2009.