The objective of the study is to analyse the current and past case law of the European Court of Justice (ECJ) regarding tax disputes based on the modern legislation of the EU countries and applicable international law to determine the concept and criteria for legal tax planning. This article provides an in-depth study of the well-known Cadbury Schweppes case (2006), including the decision of the ECJ, which laid the foundation for a new concept of examination and interpretation of tax disputes on the merits in general. The introduction of the concept of “wholly artificial arrangements” and their characteristics stipulated and determined the development of the entire field of tax planning for years to come. Other rulings of the ECJ following the case of Cadbury Schweppes have described in greater detail and more specifically the concept of “wholly artificial arrangements” under the influence of the practice of tax planning itself, determining what tax planning is legitimate and how exactly it should be distinguished from tax evasion and tax avoidance. Several research methods have been used in this study: comparative method, historical method, analytic method, inductive method. Keywords: European Court of Justice, freedom of establishment, notion of economic substance, tax disputes, tax planning, wholly artificial arrangements, tax evasion