By joining the European Union, the Republic of Croatia has made an obligation to adopt implementing regulations which govern relations between the Member States of the European Union in the field of administrative cooperation and extending mutual help in the exchange of information as well as collection of claims based on contributions and taxes and other public benefit, implementation of measures of collection, enforcement and insurance, all for the purpose of gaining the right to social security. Given the fact that the Member States have regulated the rights from compulsory insurances and vice versa, it was necessary to coordinate the procedure and to ensure equal application of regulations to all EU Member States. The topic of this paper is the coordination of competent institutions in the process of gaining social security rights. This paper will explain the procedure of mutual assistance in the billing of contributions between the Republic of Croatia and other EU Member States - applicants for collection, legal regulations which are the basis of proceedings, enforcement procedures conducted by Tax Administration officials with the goal of collecting claims, and information exchange procedures, as well as which institutions participate in the said coordinated procedures. From all the above, it can be concluded that cooperation between countries is key to the successful achievement of social security goals. The biggest obstacle in mutual cooperation is the fact that the exchange of information between the Tax Administration and other institutions takes place exclusively on paper, which is a long and uneconomical process, so the tendency in the coming period is the introduction of automation and digitalization of all international cooperation processes.