Racial segregation is the systematic separation of people into racial or other ethnic groups in daily life. Racial segregation can amount to the international crime of apartheid and a crime against humanity under the 2002 Rome Declaration of Statute of the International Criminal Court. Segregation can involve the spatial separation of the races, and mandatory use of different institutions, such as schools and hospitals by people of different races. Specifically, it may be applied to activities such as eating in restaurants, drinking from water fountains, using public toilets, attending schools, going to films, riding buses, renting or purchasing homes or renting hotel rooms. In addition, segregation often allows close contact between members of different racial or ethnic groups in hierarchical situations, such as allowing a person of one race to work as a servant for a member of another race.

Segregation is defined by the European Commission against Racism and Intolerance as "the act by which a (natural or legal) person separates other persons on the basis of one of the enumerated grounds without an objective and reasonable justification, in conformity with the proposed definition of discrimination. As a result, the voluntary act of separating oneself from other people on the basis of one of the enumerated grounds does not constitute segregation". According to the UN Forum on Minority Issues, "The creation and development of classes and schools providing education in minority languages should not be considered impermissible segregation if the assignment to such classes and schools is of a voluntary nature."

Racial segregation has generally been outlawed worldwide. In the United States, racial segregation was mandated by law in some states (see Jim Crow laws) and enforced along with anti-miscegenation laws (prohibitions against interracial marriage), until the U.S. Supreme Court led by Chief Justice Earl Warren struck down racial segregationist laws throughout the United States. However, racial segregation may exist de facto through social norms, even when there is no strong individual preference for it, as suggested by Thomas Schelling's models of segregation and subsequent work. Segregation may be maintained by means ranging from discrimination in hiring and in the rental and sale of housing to certain races to vigilante violence (such as lynchings). Generally, a situation that arises when members of different races mutually prefer to associate and do business with members of their own race would usually be described as separation or de facto separation of the races rather than segregation.