If Shakira, a Colombian pop star, marries her boyfriend, the Spanish national footballer Gerard Pique, the only unusual things about it would be that she is even more famous than he is and ten years older. Otherwise, theirs would be just a celebrity example of one of the world’s biggest social trends: the rise of international marriages—that is, involving couples of different nationalities. A hundred years ago, such alliances were confined to the elite of the elite. When Randolph Churchill married Jennie Jerome of New York, it seemed as if they had stepped from the pages of a Henry James novel; brash, spirited American heiress peps up the declining fortunes of Britain’s aristocracy. Now, such alliances have become almost commonplace. To confine examples to politicians only: the French President Nicolas Sarkozy is married to the Italian-born Carla Bruni and his Prime Minister Francois Fillon has a Welsh wife, Penelope Clarke. Nelson Mandela is married to Graga Machel (from Mozambique). Denmark’s new Prime Minister Helle Thorning-Schmidt is married to a Briton, Stephen Kinnock. And two leading female politicians of Asian countries, Aung San Suu Kyi of Myanmar and India’s Sonia Gandhi, are both widows from international marriages. In rich countries alone such unions number at least 10 million. International marriages matter partly because they reflect—and result from—globalisation. As people holiday or study abroad, or migrate to live and work, the visitors meet and marry locals. Their unions are symbols of cultural integration, and battlefields for conflicts over integration. Few things help immigrants come to terms with their new country more than becoming part of a local family. Though the offspring of such unions may struggle with the barriers of prejudice, at their best international marriages reduce intolerance directly themselves, and indirectly through their offspring. Defining what counts as international is tricky too. A wedding of a local man and a foreign-born bride is easy. But the marriage of two foreigners in a third country sometimes counts and sometimes doesn’t. Trickiest of all is how to treat the marriage of a second-generation immigrant who has citizenship of a host country (say, the child of a Moroccan in France or a Mexican in America). If such a person marries a native Frenchwoman or an American, that usually does not count as international, even though it is an alliance across ethnic lines. Conversely, if he marries a girl from his parents’ country of origin, that does count as international—but this is not a marriage across an ethnic divide and may indicate isolation not assimilation. Belatedly, answers to these questions of scale and definition are coming, chiefly thanks to the efforts of the International Union for the Scientific Study of Population (IUSSP), a professional association of demographers, and, especially, of Doo-Sub Kim, a professor at Hanyang University in Seoul who chairs its panel on cross-border marriages. Global figures remain sketchy, but marriage patterns in Asia and Europe, at least, are becoming clearer. Some tentative, often surprising, conclusions are emerging. Asia is the part of the world where cross-border marriages have been rising most consistently. According to Gavin Jones of the National University of Singapore, 5% of marriages in Japan in 2008-2009 included a foreign spouse (with four times as many foreign wives as husbands). Before 1980, the share had been below 1%. In South Korea, over 10% of marriages included a foreigner in 2010, up from 3.5% in 2000. In both countries, the share of cross-border marriages seems to have stabilised lately, perhaps as a result of the global economic slowdown. International marriages have played a significant role in modifying the ethnic homogeneity of East Asian countries. International marriages are common in much of Europe, too. Calculations by Giampaolo Lanzieri, an Italian demographer, show that in France the proportion of international marriage rose from about 10% in 1996 to 16% in 2009. In Germany, the rise is a little lower, from 11.3% in 1990 to 13.7% in 2010. Some smaller countries have much higher levels. Nearly half the marriages in Switzerland are international ones, up from a third in 1990. Around one in five marriages in Sweden, Belgium and Austria involves a foreign partner.