EN
The article aims to describe the issue of aggressive tax optimisation, which relies on avoidance or evasion of taxation by entrepreneurs. This consists in the activities stemming from the legal regulations that do not reflect the actual and reliable transactions, or actual business processes, but are directed, primarily, at lowering the taxation level instead. This is a complex and multi-dimensional issue that results in state budgets’ losses amounting to many billions every year. In his article, the author also presented the impact of such practices on the condition of public finances of several Member States of the European Union, including Poland, on the competition, as well as the quality of citizens’ lives. The issue has been analysed with regard to corporate income tax (CIT).