Ireland's rehearsal of the migration debate is being played out on the fringes of a larger global drama. The UN estimates that some 200 million people settled outside of the country in which they were born last year.
One in eight Americans and nearly one in four Australians are now foreign-born, while in Europe, the numbers who fall into the same category have soared from 10 million in 1970 to 31 million in 2000. Rates vary across the continent: immigrants represent 3.2 per cent of the population in Finland, 10 per cent in France, 13 per cent in Germany and 23.5 per cent in Switzerland.
Remittances - money sent home by migrants - are reckoned by the World Bank to have been worth more than 195 billion last year - more than double the total spent on global development aid in the same period.
Yet although the number of global migrants more than doubled between 1970 and 2000 - from 82 million to 175 million - the world's population rose from 3.7 billion to six billion over the same period, which means the migrant share of the world's population only edged up, from 2.2 per cent to 2.9 per cent.
However, migration is controversial - not because it is new (mass migration took off in the early 19th century) but because its patterns have changed. Whereas early migrants brought labour from the Old World to the New, since the second World War the movement has mainly been from the Third World to the First, and today's migrants - mostly from poor countries - are moving to a handful of rich countries with low birth rates, where they account for a large and rising share of the population. In some places there has been a backlash against this trend.
Migration, then, has become a vexed political issue: so much so, says the UN's special representative on the area, Peter Sutherland, that it is now "the key international question for this century".