The state has a legitimate right to collect all taxes which, according to the applicable tax law, belong to it, nothing more and no less. Since taxes represent one of the larger and socially most undesirable expenditures, the companies and individuals want more or less creatively avoid its payment. Because of that, the state needs certain tools to prevent such behavior. One of such tool is the legalization of the consequences of the institute of sham and avoidance transactions in the tax law field. The institute draws its strength primarily from its general and broad formulation, which allows it to capture most cases in which people are avoiding tax obligations. In doing so, the institute greatly interferes with the legal certainty and predictability of tax receivers and opens other controversial constitutional issues. In the master's thesis, the adequacy of the regulation of the sham and avoidance transactions in the tax law field is presented. In this regard, the author first presents the origin of the definition of the institute, places it in the tax law and through the development of the institute, presents its current state. In conclusion, the author presents trends in the subject area and assesses the possibilities of further development of the institute. The author also gives a comparative analysis of the commented area.