White supremacy is the belief that white people are superior to those of other races and thus should dominate them. The belief favors the maintenance and defense of any power and privilege held by white people. White supremacy has roots in the now-discredited doctrine of scientific racism and was a key justification for European colonialism.

As a political ideology, it imposes and maintains cultural, social, political, historical, and/or institutional domination by white people and non-white supporters. In the past, this ideology had been put into effect through socioeconomic and legal structures such as the Atlantic slave trade, Jim Crow laws in the United States, the White Australia policies from the 1890s to the mid-1970s, and apartheid in South Africa. This ideology is also today present among neo-Confederates.

White supremacy underlies a spectrum of contemporary movements including white nationalism, white separatism, neo-Nazism, and the Christian Identity movement. In the United States, white supremacy is primarily associated with the Ku Klux Klan (KKK), Aryan Nations, and the White American Resistance movement, all of which are also considered to be antisemitic. The Proud Boys, despite claiming non-association with white supremacy, have been described in academic contexts as being such. In recent years, websites such as Twitter, Reddit, and Stormfront, and the presidential campaign of Donald Trump, have contributed to an increased activity and interest in white supremacy.

Different forms of white supremacy have different conceptions of who is considered white (though the exemplar is generally light-skinned, blond-haired, and blue-eyed—traits most common in northern Europe, which are pseudoscientifically viewed as being part of an Aryan race), and not all white supremacist organizations agree on who is their greatest enemy. Different groups of white supremacists identify various racial, ethnic, religious, and other enemies, most commonly those of Sub-Saharan African ancestry, Indigenous peoples of the Americas and Oceania, Asians, multiracial people, Middle Eastern people, Jews, Muslims, and LGBTQ+ people.

In academic usage, particularly in critical race theory or intersectionality, "white supremacy" can also refer to a social system in which white people enjoy structural advantages (privilege) over other ethnic groups, on both a collective and individual level, despite formal legal equality.