Racial boundaries can involve many different factors (such as ancestry, physical appearance, national origin, language, religion, and culture), and may be set in law by governments, or may depend on local cultural norms.
Discrimination based on skin color,(measured for example on the Fitzpatrick scale) is closely related to racial discrimination, as skin color is often used as a proxy for race in everyday interactions, and is one factor used by legal systems that apply detailed criteria. For example, the Population Registration Act, 1950 was used to enforce the apartheid system in South Africa, and Brazil has set up boards to assign a racial category to people for the purpose of enforcing racial quotas. Because of genetic variation, skin color and other physical appearance can vary considerably even among siblings. Some children with the same parents either self-identify or are identified by others as being of different races. In some cases, the same person is identified as a different race on a birth certificate versus a death certificate. Different rules (such as hypodescent vs. hyperdescent) classify the same people differently, and for various reasons some people "pass" as a member of a different race than they would otherwise be classified in, possibly avoiding legal or interpersonal discrimination.
A given race is sometimes defined as a set of ethnicities from populations in neighboring geographic areas (such as a continent like Australia or a subcontinental region like South Asia) that are typically similar in appearance. In such cases, racial discrimination can occur because someone is of an ethnicity defined as outside that race, or ethnic discrimination (or ethnic hatred, ethnic conflict, and ethnic violence) can occur between groups who consider each other to be the same race. Discrimination based on caste is similar; because caste is hereditary, people of the same caste are usually considered to be of the same race and ethnicity.
A person's national origin (the country in which they were born or have citizenship) is sometimes used in determining a person's ethnicity or race, but discrimination based on national origin can also be independent of race (and is sometimes specifically addressed in anti-discrimination laws). Language and culture are sometimes markers of national origin, and can prompt instances of discrimination based on national origin. For example, someone of a South Asian ethnicity who grew up in London, speaks British English with a London accent, and whose family has assimilated to British culture might be treated more favorably than someone of the same ethnicity who is a recent immigrant and speaks Indian English. Such a difference in treatment might still informally be described as a form of racism, or more precisely as xenophobia or anti-immigrant sentiment.
In countries where migration, unification, or breakup has occurred relatively recently, the process of ethnogenesis may complicate determination of both ethnicity and race, and is related to personal identity or affiliation. Sometimes the ethnicity of immigrants in their new country is defined as their national origin, and span multiple races. For example, the 2015 Community Survey of the United States Census accepted identification as Mexican Americans of any race (for example including Native Americans from Mexico, descendants of Africans transported to New Spain as enslaved people, and descendants of Spanish colonists). In surveys taken by the Mexican government, the same people would have been described as indigenous, black, or white (with a large number of people unclassified who might be described as Mestizo). The U.S. census asks separate questions about Hispanic and Latino Americans to distinguish language from racial identity. Discrimination based on being Hispanic or Latino does occur in the United States, and might be considered a form of racial discrimination if "Hispanic" or "Latino" are considered a new racial category derived from ethnicities which formed after the independence of the former colonies of the Americas. Many statistical reports apply both characteristics, for example comparing Non-Hispanic whites to other groups.
When people of different races are treated differently, decisions about how to treat a particular person raise the question of which racial classification that person belongs to. For example, definitions of whiteness in the United States were used before the civil rights movement for purpose of immigration and ability to hold citizenship or be enslaved. If a race is defined as a set of ethnolinguistic groups, then common language origin can be used to define the boundaries of that group. The status of Finns as white was challenged on the grounds that the Finnish language is Uralic rather than Indo-European, purportedly making the Finns of the Mongoloid race. The common American notion that all people of geographically European ancestry and of light skin are "white" prevailed for Finns, and other European immigrants like Irish Americans and Italian Americans whose whiteness was challenged and who faced interpersonal if not legal discrimination. American and South African laws which divided the population into whites from Europe and blacks from sub-Saharan Africa often caused problems of interpretation when dealing with people from other areas, such as the rest of the Mediterranean Basin, Asia, North Africa, or even Native Americans, with classification as non-white usually resulting in legal discrimination. (Some Native American tribes have treaty rights which grant privileges rather than disadvantages, though these were often negotiated on unfavorable terms.) Though as an ethno-religious group they often face religious discrimination, the whiteness of all Jews was also challenged in the United States, with attempts to classify them as Asiatic (Palestine being in western Asia) or Semitic (which would also include Arabs). The actual ancestry of most Jewish people is more varied than simply ancient Hebrew tribes. As the Jewish diaspora spread across Europe and Africa over time many Jewish ethnic divisions arose, resulting in Jews who identify as white, black, and other races. The reunification of diverse populations in modern Israel has led to some problems of racial discrimination against dark-skinned Jews by light-skinned Jews.