The subject of this thesis is efficiency of the legal framework of the European Union in stimulating mobility of posted workers on the Internal Market of the EU. Making of this legal framework that regulates mobility of posted workers in the framework of providing services, is one of the longest running subjects discussed in the processes of the EU integration. Acceptance of the Directive which introduced the rule of “equal pay for equal work” led to a substantial liberalization of labour markets for posted workers in the EU. As a result, posted workers have since then had the highest growth rate of all forms of mobility of labour force in the EU. Analysis of available data on mobility of posted workers at the level of EU-14 “Old” Member States and EU-13 “New” Member States concluded that more advanced Member States of the EU are predominant in the mobility of posted workers, either as receiving or as sending Member States. This is contrary to what many feared will happen with the entry of the Central and Eastern European countries into the EU, when it had been expected that these Member States will be responsible for the largest share of posted workers. It has also been shown that in the light of short term aspects of posted workers, more advanced Member States often used this instrument in order to correct sectoral and geographical imbalances of their economies. Legal framework of the EU introduced the possibility for posted workers to work in two or more Member States of the EU, while maintaining their social and labour benefits. That in turn had as a consequence a change in the way companies conducted their businesses on the Internal Market of the EU. Posted workers, with all the advantages that they are having on future development of the Internal Market of the EU and with the highest growth rates of all types of labour mobility, still account for only 0.9% of the total labour force in the EU.