The tax system contains various modalities of public revenues that are established and set by the state. Given the complexity of the tax system, there are differences between established tax systems. Which means that each tax system is unique, independent and enabled in a number of different compromise situations. Given its individuality and specificity in each country, the tax system of the Republic of Croatia is modern and in accordance with the principles of the European Union. It has been established and is based on the Constitutional and legislative system. In tax arrangements, we most often find similarities with the tax systems of other member states. Taxes are, as a rule, the most generous revenue of any state. The tax system is the totality of all taxes and tax regulations in a state. In practice, there are a large number of different individual types of taxes. Given the changes that may occur in the country, it is necessary to properly apply tax policies and principles. Also, as a major change and modernization, the Tax System of the Republic of Croatia achieved by modernization and application of information and communication sciences in business. Therefore, in addition to the usual way of exercising their rights, natural and legal persons are enabled to submit applications, communicate and exercise their rights electronically. Therefore, the tax system in the Republic of Croatia (hereinafter the Republic of Croatia), the principles on which the tax system is based, will be analyzed. Tax groups in the Republic of Croatia will be determined, with an emphasis on Income Tax.