The Concept of worker is the gateway to the access to the protection of labour and social security law. The Court of Justice of the European Union first defined this concept in the field of the Free Movement of Workers in the Lawrie-Blum case. The scope of this article is to compare the definitions used by the Court in the fields of the free movement of workers and in the Social Policy Directives, in order to ascertain to which extent they can differ. Our in-depth analysis of the case law offers a nuanced picture. On one hand, it highlights that the Court tries to extend the application of the Lawrie-Blum formula to Directives which do not refer back to the national definitions of a worker, but that specificities remain in this area, like the emphasis on the link of subordination. On the other hand, for Directives referring to a national concept of workers, the Court began recently to state that, even if the competence of the Member States on this question must be acknowledged, it is not limitless.