Muir Island is a small, fictional Marvel Comics island off of the northern coast of Scotland. It plays a prominent role in the Marvel Universe, as it is home of earth's largest and most comprehensive mutant research complex, which was founded and by Dr. Moira MacTaggert in order to find help for her young son, Kevin, who was the most powerful and destructive mutant ever to be born.

Because of its wealth of knowledge on various mutants, their abilities, and other mutant-related issues and concerns, such as the Legacy Virus, as well as its one-time housing of the superhero team, Excalibur, the island and its research center have come under attack by villains numerous times in its history. Magneto, the Acolytes, the Shadow King, Galactus, and Kevin MacTaggert, who eventually became known as Proteus, have all invaded Muir Island at one point or another.