The “color line” is not fixed but ripples through time, finding expression at distinct stages of our development as a nation. As the meaning of race has changed over time, its burdens and privileges have shifted among population groups. At one time in our history, for instance, the Irish and Italians were considered “non-White,” along with other immigrants who were not descendants of the early Anglo-Saxon Protestant settlers. In this issue of the Journal, Gerald Oppenheimer traces the color line through the course of American history.1 He demonstrates how the original language of White racial differences began with the anxious response of early Americans to waves of immigration, beginning in the 1840s when the Irish (or Celts) entered US ports, followed by nationals from Central, Southern, and Eastern Europe. Over time, the descendants of these “White ethnic groups” became the monolithic Caucasian race, the majority population, superior in all respects to the Black people of African descent.1