It would be simplistic to see intra-EU mobility as just a strategy, by governments and employers, to lower labour costs and weaken trade unions, according to the traditional Marxist view of the ‘reserve army’ (Castles and Kosack, 1973). In fact, wages seem to have been affected only marginally in the EU 15, even in sectors with most new foreign workers (Briicker et al., 2009). In any case, real wages had already been stagnant in Western Europe for a while, and unions declining, so there was no urgent need for EU employers toimport foreign labour to stop wage or union growth. Sommers and Woolfson (2008) have argued that by recurring to mass migration, the EU is aping the US growth model of the last 30 years, based on the attraction of cheap and flexible foreign labour. But more than low costs, the specific attar ctive feature of the new labour supply relies exactly on their ‘mobility’ which offers a corrective to the long-blamed ‘sclerosis’ of European labour markets.