Social policy is one of the EU policies shared by the EU and the Member States. The aims of EU rules in the field of social policy include protection of the working conditions of workers, on the one hand, and prevention of social dumping between undertakings from different Member States on the other hand. The EU primary and secondary law relating to social policy uses the term “worker.” However, contrary to the national laws of the Member States, there is no definition or explanation of this concept. National laws of Member States provide different definitions of the term “worker” or “employee” which can lead to different levels of protection for workers under the national legislations of EU Member States. For this reason, the concept of “worker” for the purpose of EU social policy may not be interpreted differently according to the law of Member States but has an autonomous meaning specific to EU law.