Abstract: The two main functions of the concept of working time - quantifying the remuneration and health and security at work protection - are found together or separately in the laws of the member states while EU law regulates working time only for the purpose of protecting health and safety at work; when Member States adopt a single regulation on working time, it may define this concept more narrowly or broadly than EU regulation. In disputes before them, when the courts of the Member States have to apply both national and EU law, they are put in a position to bring the concept of working time under national law within the limits of EU regulation. The article examines the situations in which national courts may find themselves in this pr...