In this paper, the research problem is tax evasion in EU countries. High tax rates, the complexity of tax systems, activities within the shadow economy and the presence of tax havens contribute to its increase. It creates major consequences, such as a reduction in the state budget, and thus a reduction in investment in public services and infrastructure. It causes damage not only to the state, but also to the entire society. First, the research goal of this final paper is to clarify the concept of tax evasion, the reasons that lead to its occurrence, the forms in which it appears and finally its consequences. Other goals are to determine the effect of tax evasion on EU countries and the effectiveness of measures to combat it. The results of the research lead to the unmistakable conclusion that tax evasion is a ubiquitous problem within the countries of the European Union and that large losses have occurred under its influence. Better cooperation between countries, simpler tax systems and stricter legislation and various measures are needed to combat it. The most important measures are: the introduction of data recording technologies, electronic invoicing and limiting the cash economy.