The 2004 and 2007 EU enlargements led to the relocation, over the period 2004 to 2010, of about three million workers from the new EU member states to the old. The free mobility of workers in the enlarged EU provided a wider set of possibilities for its citizens and improved the allocative efficiency of EU labour markets (Kahanec and Zimmermann, 2010). The receiving countries gained additional ‘hands and brains’ without being generally affected in terms of natives’ aggregate wages or employment (Kahanec, 2013); the sending countries, in turn, were relieved of labour slack and benefited from remittances. ‘Brain drain’ has been a potential risk for the sending countries, but the literature actually points to the possibility of ‘brain gain’, which may occur when migrants return to their home countries with additional skills acquired abroad or when the home population invests more in education in expectation of higher returns due to the possibility of using skills more freely abroad (see Zaiceva and Zimmerman, forthcoming). Similarly, although the down-skilling into jobs below a worker's qualifications that characterizes much of post-enlargement migration appears undesirable, it is unclear whether real inefficiencies vis-à-vis feasible counterfactual scenarios have materialized (Kahanec, 2013). 1