Tax is a form of forced giving imposed by the state, without intentional direction and without direct counteraction. The tax system of the Republic of Croatia is regulated by laws and special regulations, which of course must be harmonized with the guidelines of the European Union. Given the frequent variability of tax laws, taxes are constantly becoming the subject of debate. The tax system should be as simple as possible, but in the case of the Republic o f Croatia this is not the case, especially when taxing second income. To sum up, this document investigates the taxation of second income in more detail. The specifics of taxes, types and principles of taxation are stated. Examples will show the taxation of second income in the Republic of Croatia and the latest changes in the tax law will be listed.