One of the key features of the European Union (EU) is the establishment of an internal market. This entails not only the free movement of goods and capital, but also the free movement of workers and services and the freedom of establishment. These latter freedoms, taken together, mean that within the EU a company that transfers workers to another member state cannot be obliged to offer them a local contract and that there are no generally applicable controls as to the conditions of employment prior to admission to the country and/or the labour market. In the EU, the task of ensuring a certain measure of protection for such migrant workers themselves while preventing unfair competition based on differences in employment conditions between local workers and migrants is delegated almost exclusively to the rules on applicable law, which have to a large extent been harmonized in Articles 8 and 9 of the Rome I Regulation and the Posted Workers Directive (PWD). As this chapter explains, the choice of law rule in private international law focuses on providing (ex post) justice in the individual case and is poorly equipped to manage migration. The system of ex ante overriding mandatory provisions is heavily curtailed by the free movement of services. Moreover, there is an uneasy match between the interests informing private international law and the interests of the internal market, which is not likely to be resolved in the near future.