In this final paper, the changes in the Customs system of the Republic of Croatia are discussed. The goal is to demonstrate the mode of operation and structure of the Customs system of the Republic of Croatia before and during the adaptation of joining the European Union and also after its entry. The selection of the theme is associated with the overall economic problems of our country. The Republic of Croatia became a full member of the European Union in July 2013. The paper is divided into five chapters. In the first, introductory chapter, thesis that will be argued and explained in this paper are introduced. The second chapter deals with the characteristics and the concept of customs. The third chapter covers the Customs system of the Republic of Croatia, including customs policy, customs regulations, organization of the customs administration, the powers of customs officers and the procedure of customs clearance of goods.The fourth chapter is covered by the tariff policy of the European Union, its objectives and basic principles, a unique customs declaration and strategy of development of the European Union in the field of customs policy. In the final, fifth chapter, the Croatian customs system before and after joining the European Union is processed.