The free movement of persons, besides the free movement of goods, capital and freedom to provide services, is a fundamental freedom that enables the functioning of the single market of the Europien Union. In order to enable the free movement of persons at the EU level, a system of ruls for the coordination of the social security system was created, whereby such a system does not replace the national legislation of the Member States. Due to the differences in the social security systems among the Members States arising from their traditional social policies and territoriality principle, and in other to avoid unequal position of persons who use the right of freedom of movement, loosing or not exercising their social rights, the European Union regulates the rules through regulations with social security systems, which from part of the European acquis from the very beginnings of integration. The goal of this rules is not the harmonization of different social security system in the Member States, but coordination, that is, mutual cooperation in the field of social security among the Member States. After accesion to the European Union, the Republic of Croatia determines the competent bodies, institutions and liaison bodies in the implementation of EU Social Security Coordination Regulations and determines the manner of participation of Croatian representatives in the bodies and expert committees of the European Commission responsible for these issues. The Croatian Pension Insurance Institute, as one of the competent institutions and liaison bodies, and are the subject of this work, together with EU Social Security Coordination Regulations and it's basic principles, has a significant role in the coordination of the realization of the rights to old-age benefits, invalidity benefits, survivors' benefits for family members, as well as benefits for work-related injuries, professional diseases, and family benefits, i.e. child allowance.