The United States is in the midst of its fourth major wave of immigration. Today's wave is the largest in absolute numbers, although not as a proportion of the total population. Unlike in previous waves, today's immigrants come from every inhabited continent and represent just about every country in the United Nations. As in previous waves, there is a profound ambivalence about immigration among the American public. Historically, Americans have seen their own immigrant forebears through rose-colored glasses while raising serious concerns about the contributions of current immigrants and the extent to which they will assimilate our values, language, and experiences.

This ambivalence has made immigration policy one of the most difficult on the U.S. political agenda. In the past three Congresses, the Senate and House of Representatives have debated immigration reform but have failed to come to consensus about the policies needed to address today's challenges. The difficulties they are experiencing are by no means new. Immigration reform has always been a difficult issue, requiring years of debate before any comprehensive changes are adopted. Although the problem is often described as a contest between pro- and anti-immigration forces, the reality is much more complex. Even among those who favor large-scale immigration, there are profound differences in views on the purposes of immigration and the contributions that immigrants bring to the country. Understanding the historical roots of American immigration, and American attitudes toward immigrants, helps to place today's policy debate into perspective and provides important insights into the reforms needed to address current problems and opportunities.