The thesis focuses on one of the key issues of the EU law – State aid law and its applicability to one of the most sensitive areas of national competences – tax measures. This is the field of EU competition policy in which keeping the balance between the Member States and the Union interests is extremely difficult due to the divergent policy goals of the participants. Competition rules vividly play a significant role in the EU economy which enables market players and consumers to gain profits and benefits from their divergent activities. The main idea behind competition policy is that a market-based economy provides the best guarantee for increasing EU citizens living conditions and enhancing the competitiveness of the European economy. Accordingly, State aid law discipline also forms one of the crucial elements of the competition law by having in mind the aim to prevent distortion of competition since not only private anti-competitive behaviour, but also State intervention in the Single Market can distort free competition. Given that, the thesis intends to demonstrate whether the control rules (State aid control) are necessary for providing the truth and avoiding surprise and whether the “Commission’s grace” is compatible with the Union law. Moreover, the paper illustrates the development of the scope of the legal framework since the establishment of the ECSC up until the present time. Additionally, the most important attention will be paid for the applicability of Article 107 TFEU to tax measures through examining whether the derogation method and the selectivity criterion, established by the case-law of the CJEU and the Commission’s practice, treat the things that are alike, alike and things that are unlike, unlike in proportion of their unlikeness.