The Pew Forum on Religion and Public Life has just published a report on the religious affiliation of international migrants. Pew's research shows that there are vastly more Christian immigrants in Europe than Muslims (26 million, or 56% of the foreign-born population, versus 13 million). However, if one excludes internal migration within the European Union, the shares are much closer: 42% Christian to 39% Muslim, respectively.
Here's the spotlight on Europe.