The thesis deals with the effects of the ECJ-judgements Viking, Laval, Rüffert and Commission/Luxemburg on European Law as well as the Private Law of the Member States. In the first part it focuses on Private International Law in labour relations, laid down in Art 8 and 9 Rome-I Regulation (labour contracts), Art 9 Rome-II Regulation (labour disputes) and the EU Posting of Workers Directive (96/71/EC). The Directive establishes which terms and conditions of employment are applicable to a worker who, for a limited period, carries out his work in the territory of a Member State other than the State in which he normally works. This question is deeply intertwined with the right of a workers employer to provide services within the EU. What is also presented is the Austrian transposition of the Directive, which was revised in 2011. Subsequently the aforementioned cases are analysed in the second part of the thesis, giving a broad overview of their reception in academia. Part three starts with presenting the effects of the ECJ-judgements on the interpretation of the Posting of Workers Directive and analysing its relation to the freedom to provide services. In a next step it is shown that after Viking and Laval trade unions are bound by their counterparts freedom of establishment and freedom to provide services when taking collective action. In the same two decisions the ECJ recognised the trade unions fundamental right to take collective action, including strikes. Due to the Treaty of Lisbon, which transformed the fundamental rights structure within the Union, Art 28 of the Charta of Fundamental Rights as well as Art 11 ECHR nowadays guarantee this right as well. Subsequently the Courts weighting of the interests of workers and trade unions respectively as well as those of companies is criticized. Thus another model of fair balance is proposed. Finally, the effects of the four decisions on the European Social Model are discussed.