The expansive Sonic the Hedgehog universe, spanning over three decades, encompasses numerous mainline games, spin-offs, and adaptations.  Determining the chronological order of these titles has been a source of ongoing discussion and confusion among fans, particularly concerning games like Sonic CD and the implications of time travel in entries such as Sonic Generations and Sonic the Hedgehog 2006.

The recent release of Sonic Frontiers in 2022 further complicated the timeline by introducing significant lore elements, including the backstory of the Chaos Emeralds and connections to previous titles like the Sonic Adventure duology.  Fortunately, Sega has responded to fan inquiries by publishing an official timeline on the Sonic the Hedgehog website.

This official timeline details the Sonic universe's history from prehistoric times, beginning with the birth of Light Gaia and Dark Gaia from Sonic Unleashed (Sonic World Adventure in Japan), and extending to the altered future depicted in Sonic the Hedgehog 2006. Key prehistoric events such as the Ancients' arrival (Sonic Frontiers), Dark Gaia's rampages, and the Echidna Tribe's decline (Sonic Adventure) are also chronicled.

The timeline progresses to more recent events, including Professor Gerald Robotnik's story and the ARK from Sonic Adventure 2, and the experiments leading to the creation of Solaris in Sonic the Hedgehog 2006. It then seamlessly transitions into the classic era, starting with the original 1991 Sonic the Hedgehog.  Notably, the timeline confirms that Sonic CD precedes Sonic the Hedgehog 2 and other classic 2D titles.  It also places the more recent retro-inspired titles, Sonic Mania (2017) and Sonic Superstars (2023), before the 'Modern Era,' which begins with Sonic the Hedgehog 4.

The Modern Era games are generally listed in release order, incorporating spin-offs like Sonic Shuffle and the Sonic Riders series. While not every Sonic game is included, the timeline provides crucial context for the placement of many key titles.  This official timeline serves as a valuable resource for fans and lays the groundwork for future Sonic games to expand upon the already rich lore and characters of the franchise.