NATIONAL BORDERS SEEM increasingly porous. Nearly 215 million persons now live in a country where they were not born, so immigrants account for about 3 percent of the world’s population. It is not surprising that the surge in large- scale international migration increased the foreignborn share of the population in a traditional immigrant- receiving country like the United States— from 6 to 13 percent in the past 30 years. What is surprising is that the foreign- born share now stands at record levels in countries that have little historical experience with immigration: 9 percent in Portugal, 10 percent in Norway and the United Kingdom, 13 percent in Germany, 14 percent in Spain and Sweden, and 16 percent in Austria (United Nations 2011). Much of the developed world is increasingly composed of “nations of immigrants.”