The main objective of this paper is a comparative analysis of the tax system of the Republic of Croatia and selected countries of the European Union. With the elaboration of the theoretical framework of tax systems, this paper compares secondary data aggregated from the sources of a relevant literature. The goal is to define taxes, present types, characteristics and principles in order to provide a more detailed insight into the tax system of the Republic of Croatia and selected countries of European Union. The paper examines the effectiveness of tax systems in the real-world conditions. The paper also emphasizes the importance of tax harmonization throughout the territory of the European Union. The research section of this paper conducts of a comparative analysis of the ratio of tax revenues as a percentage of gross domestic product (GDP), tax rates adjustment in comparison with the EU directives and the correlation between the amount of tax revenues and economic growth rates. The analysis focuses on features of the corporative income tax, personal income tax, and value added tax due to their extraordinary widespread distribution and importance to most taxpayers. For the purposes of comparison of tax systems European Union Member States, the Republic of Austria, the Republic of Ireland and the Czech Republic, have been selected as research relevant. Austria and Ireland are members of the euro area and their national currency is the Euro. The Austrian tax system is characterized by high tax rates while in contrary Irish tax system has one of the lowest tax rates in Europe. The Czech Republic and Croatia have many similarities, and thus their tax systems and tax rates coincide. They are members of European Union but not members of the euro area, concluding, their domestic currencies are Czech Koruna and Croatian Kuna. In conclusion of this paper, the results obtained through the research are summarized as well as the recommendations for the practice.