The Brotherhood of Mutants (originally known as the Brotherhood of Evil Mutants) is a fictional group of mutants appearing in American comic books published by Marvel Comics. The Brotherhood are among the chief adversaries of the X-Men. While the group's roster and ideology have varied from incarnation to incarnation, most versions of the Brotherhood are generally founded and led by the mutant Magneto as a super villain team or mutant supremacy organization that uses extreme methods to fight human prejudice.

Unlike the X-Men who believe that humans and mutants can coexist peacefully, the Brotherhood generally views humanity as an inferior close-minded species that will never accept mutants out of fear of their powers. Among the Mutants who are frequently depicted as members of the Brotherhood are Mystique, Toad, Blob, Pyro, Mastermind, Quicksilver, and Scarlet Witch.

The original Brotherhood was depicted as Magneto's primary allies in his early battles with the X-Men in comics published in the 1960s. The original Brotherhood was ultimately disbanded, with Quicksilver and the Scarlet Witch going on to become members of the Avengers. In 1981, the Brotherhood of Mutants was revived under the leadership of Mystique, while the group's most visible incarnation during the early 1990s was led by Toad.

The Brotherhood of Mutants has also appeared on several animated series featuring the X-Men and has been Magneto’s group in the X-Men film series.

The original Brotherhood of Evil Mutants was created by writer Stan Lee and artist/co-writer Jack Kirby and first appeared in X-Men #4 (March 1964).

While later incarnations of the Brotherhood promoted the group's existence as a political and ideological rival to Professor Charles Xavier's dream of peace with humans, the group was originally conceived as simply a small, but powerful army of minions gathered by Magneto to aid in his schemes for world domination. But since the group's second incarnation, the group has become a much more politically motivated group designed for use of violence to provide justice and lead a 'mutant revolution' against mankind.

One of the greater ironies of the group has been its use of "Evil" in its name. When his decision to name the group was brought up in an interview, Stan Lee simply said "We were kind of corny in those days." Since the early 1990s, writers have attempted to explain this away by having Toad describe it as irony, based upon the perceived notion that all mutants are "evil." Later writers have opted instead to simply drop "Evil" from the group's name and refer to the group as "The Brotherhood of Mutants" or simply the Brotherhood. In Earth-X, Uatu explained that Magneto chose it so that, as the opposing side, Charles would be forced to assume the role of "Good," and that Magneto believed that by locking Charles into absolutes of morality, he could manipulate him.

Many of the group's members have been shown to be past victims of anti-mutant prejudice, which has made the group a haven for many mutants who feel they are outcasts and pariahs. While many of these outcast mutants have willingly embraced the violent aspects of the Brotherhood's ideology, several have ultimately rejected it and left the group because of it. Most notably, Quicksilver and the Scarlet Witch left the group due to their disillusionment with Magneto's ideology to join the Avengers, a group of heroes dedicated to protecting the world as opposed to ruling it.