The purpose of the undergraduate expert thesis „The customs duty system of the European Union“ is to explore the role of EU customs in administrative terms and its impact on the international market. By collecting all the relevant data and studying available literature on tariffs and the customs territory of the European Union, it is found the great complexity of the customs duty system as well as the challenge to operate overall process in an accurate way. Furthermore, the great effort of the Customs policy has been noticed in trying to reach the sustainable symbiosis of the European Union member states, despite their distinctive cultural and economic backgrounds. Moreover, it is quite important to point out the main need and the idea of the unique common market, where every member of the European Union could be competitive and could get the equal opportunity to present well in front of the potential demand and third parties on the international market. Therefore, the greatest purpose of introducing the customs system has been recognized in the need of creating the feeling of togetherness and equality of the European Union citizens in getting rights for equal and fair business trade. All trading rules between country members are clearly defined. Any possible violation is punished by the European institutions in order to avoid inconveniences and eliminate unnecessary costs. By joining the European Union, the Republic of Croatia became part of the unique market and has adopted regulations based on the European Union's tariff regulations that are combined with regulations of the Republic of Croatia in order to operate simultaneously. Trading between Croatia and the EU's members is not under duty control. However, goods that do not have the status of commodity Community are an exception in such situations. Any goods specified for import or export from the customs territory must be notified and send through electronic platform. To conclude, The Republic of Croatia as a full and equal member of European Union meets the standards of European policy.