The book follows the development and creation of international tax rules in response to the emergence of increasingly diverse ways of tax avoidance, especially in cases where an international element is present. By describing the problem as a bundle of maneuvers directed at tax avoidance, I elucidated the development of relevant legal instruments. The establishment of higher-level legal instruments began primarily with the BEPS Action Plan, and then with the European Union's response to the requested measures by adopting a Directive laying down rules against tax avoidance practices that directly affect the functioning of the internal market. The book elaborates in detail some open issues that followed the adoption of the said Directive in case law. The Specific Anti-Tax Avoidance Rules (SAARs) and the General Anti-Tax Avoidance Rule (GAAR) constitute the most important subject of book interest, with special emphasis on GAAR. Finally, I endeavor to analyze the impacts on the national tax legislations of Croatia, Italy and Germany in terms of the implementation of the new harmonized rules at the level of the European Union.