The study starts with the assumption that realizing sustainable and integrated development of European Union countries, through the building of a competitive and knowledge-based market economy, is significantly hindered by the lack of an appropriate tax system. With this in mind, the study supports the thesis that it is necessary to implement an optimal tax system in the EU, defined as a collection of taxes which maximize the welfare of society. To support this thesis, the study presents the principles of a methodology for determining the basic components of this system, they are: taxes on corporate and personal income, VAT and capital tax, the functions of these taxes and guidelines on tax rates.