This thesis deals with a systematic analysis of taxes and tax systems of two countries that are at first glance very similar, but different in terms of efficiency and type of tax policies and tax system as a whole. The focus of this thesis is based on the highlighting of individual elements that make a particular tax system effective. At the very beginning, the basic facts and principles on which the tax system is based will be reviewed, and in the elaboration part, will be made a thorough analysis of the tax system of the Republic of Croatia and Slovakia. The tax system of each country has certain specificities that make it different from the tax systems of other countries and make it adapted to the needs of the national economy. Furthermore, the research part of the work will analyze important indicators such as: the share of tax revenues in GDP and the structure of tax revenues, a graphic overview of tax rates and tax revenues in the observed period for both mentioned countries. In that way the importance of the effects of tax policies and reforms on the stability and prosperity of the national economy is emphasized. During the preparation of the will be used secondary data from various scientific articles, publications and other relevant sources. The purpose of this paper is to highlight all the important similarities and differences between the tax systems of Croatia and Slovakia, and to achieve that every reader after reading this paper has a clear idea of how much the simplicity and efficiency of the tax system has an important impact on the development of the economy of a particular country. Comparative analysis of the tax systems of the Republic of Croatia and Slovakia will give a clear presentation of the differences between the systems and will highlight the main characteristics that make the tax system as simple, efficient and as well adapted to the specifics of the national economy as possible.