The series follows Sonic, an anthropomorphic blue hedgehog who can run at supersonic speeds and curl into a ball to attack enemies. In most games, Sonic must race through levels, collect power-up rings, and avoid obstacles and enemies. His primary antagonist is Dr. Ivo 'Eggman' Robotnik, a mad scientist who wants to conquer the world and build his 'Eggman Empire'.

Often, Eggman seeks the Chaos Emeralds, seven mystical gems that possess infinite power. Sonic and his friends—such as Tails, Knuckles, and Amy—must stop Eggman from obtaining these emeralds and enslaving the world's animal population inside his robots (Badniks). The franchise spans multiple universes, including games, comics, and cartoons, each adding depth to the lore while maintaining the core conflict of nature versus mechanization.

The setting of the series varies, sometimes taking place on a fantasy world known as Mobius, and other times on a stylized version of Earth. Both versions feature a mix of lush natural environments and futuristic cities.

Green Hill Zone: The most iconic location in the franchise, characterized by checkered brown soil, loop-de-loops, palm trees, and vibrant blue skies. It represents the beauty of nature that Sonic protects.

Chemical Plant Zone: An industrial nightmare filled with toxic "Mega Mack" fluids and twisting pipes, symbolizing Eggman's pollution and disregard for the environment.

Angel Island: A floating island in the sky, kept aloft by the power of the Master Emerald. It is the home of Knuckles the Echidna and the ruins of an ancient echidna civilization.

The Death Egg: Dr. Eggman's ultimate weapon, a massive space station the size of a moon (bearing a resemblance to his own face), built to project his power globally.

Various locations on Earth/Mobius, spanning from tropical islands to space stations.