The diploma thesis deals with the issue of tax evasion and the related tax morale of taxpayers. The main aim of this thesis was to identify the factors that influence taxpayers' decisions in the European Union on the issue whether they justify cheating on tax or not. Dependence and effect of selected factors was determined by analysing data from the European Value Study from 2017. The thesis is focused mainly on the Czech Republic, Poland and Spain. The dependence of the willingness to justify cheating on tax has been demonstrated, with a few exceptions, for all selected factors. It was found that not only demographic factors (gender, age), but also other socio-economic and institutional factors (religion, willingness to defend their countr...