Freedom of movement of workers within the European Union is one of the four fundamental freedoms on which the internal market of the European Union has been established, which benefits citizens of the European Union as well as the Member States, but also the competitiveness of the European economy as a whole. The principle of freedom of movement for workers is laid down in Article 45. of The Treaty on the Functioning of the European Union as primary legislation, however, is also covered by secondary legislation as well as by diverse case-law. The freedom of movement of workers is subject to the restrictions laid down in the Treaty on the Functioning of the European Union. Restrictions shall be justified only on grounds of public policy, public health and public security. At the same time, Article 45 also States that employment in public services is also one of the limits of this freedom. The concept of “worker”, which is not explicitly defined by the primary or secondary legislation of the European Union relating to this field, is also relevant to this subject. Case law reveals there are numerous doubts and problems in the interpretation of concepts such as workers but also situations where restrictions on that freedom are justified. Through various examples from the case-law, we can conclude that it is necessary that they should be based on the personal conduct of an individual who must pose a genuine and serious threat to public policy and public security.