- "We have a legal right to be here. This land was given to us by the U.S. Government."
- ―Magneto to an army ranger captain
Located a few miles from the coast of the eastern seaboard, Genosha was an island of relatively small size, making it practically undetectable. Appearing rather nondescript from the outside, inside, the island was heavily fortified by Magneto. The interior of the island was reinforced with steel girders, heavy titanium furnishings, and metallic walkways that could be manipulated by the master of magnetism. The base was also well equipped, providing several accommodations for the Brotherhood and it's members. Such areas included lodging, a mechanical workshop, a helipad, a boat dock, an interrogation room, and holding cells for prisoners such as Senator Kelly. The island also contained a private sanctuary for Magneto, where he would often plot his schemes. As seen in the Magneto prequel comic, the sanctuary also contained a room equipped with several televisions that lined the walls; here, Magneto would monitor important news broadcasts.
Magneto would come back to the island with Pyro and Mystique after the events of Alkali Lake. Shortly after Mystique would get captured out on a mission. Magneto would stay here trying to find her and soon discovering about the Mutant Cure. Pyro would eventually locate Mystique in the Prison Convoy and the pair would leave to rescue her. After recruiting Multiple Man, Juggernaut, and the Omegas to his new Brotherhood of Mutants, Magneto returns to the island, where Callisto tells him about where Jean Grey is. The team later establishes a new base afterwards in the The Forest.
In 1992, Magneto established the island nation of Genosha as a sanctuary for mutants, where they can live in peace far away from the prosecution of humans. Eventually, Magneto comes into contact with Jean Grey, when she comes to the island looking for Erik's help. Erik runs the island with the help of Selene and Ariki.
- In Rise of the Phoenix - The Making of Dark Phoenix, several cast and crew members pronounce Genosha with a hard "G". In the comics and several adaptations, Genosha is pronounced with a soft "G".