This European Commission Paper shows that migration-induced reallocation of labour resources across countries following the 2004 EU enlargement process has already brought sizeable economic benefits for the enlarged EU. It would be naïve to think, however, that all European citizens have won from the enlargement the authors say. At the level of specific skill groups, for example, there is the potential for income losses for the low skilled in the “receiving” countries and for medium to high skilled workers in the “sending countries”.