The United States of America is a nation of immigrants, as approximately 50 million people migrated to the United States over the years. Today, there can be found diverse ethnic groups representing every nationality, race, and religion. Making sense out of this dynamic mosaic of groups is essential if we are to understand American society. Assimilationism, ethnic pluralism, and ethnic conflict theory constitute the three principal schools of thought on race and ethnic relations. It is argued that each theory is only a partial explanation concerning ethnic/racial relations, but each makes up for some of what the other theories lack. Traditional assimilation theories seem preoccupied with the relatively voluntary migration of European immigrants into the United States. Opposit to the assimilationism is ethnic pluralism, a situation in which each group maintain its distinctive identity, subculture, and infrastructure. Both assimilationism and ethnic pluralism had largely emphasized European, white immigrants, thus, leaving the experiences of ‘the racial minorities’, such as Afro-Americans, Latin Americans, Native Americans, and Asian Americans, unaccounted for. Conflict theories are best fit to explain the situation of the racial minorities. There are three versions of conflict theory: internal colonialism, the split-labor market theory, and middleman minorities. The dual themes of adaptation and stratification run through American history as well as American society. It is found to be useful to distinguish racially defined minorities from ethnically defined minorites, because the adaptation processes of the non-white immigrant groups seem to differ substantially from the white, European immigrant groups. In this respect, the United States can be regarded as a racially stratified society.