The GDPR aims to harmonize the data protection rules across the EU and to ensure consistent and effective enforcement of those rules. However, the GDPR also recognizes that there may be some differences in the interpretation and application of the law among the member states, depending on their national legislation, culture and practices. Therefore, the GDPR introduces the concept of the “main establishment” of a controller or processor, which is the place where the decisions on the purposes and means of the processing of personal data are taken in the EU1. The main establishment determines which national supervisory authority will act as the lead authority for the cross-border processing activities of that controller or processor, and which national law will apply in case of a dispute or a complaint2. The Article 29 Working Party, which is an advisory body composed of representatives of the national supervisory authorities, the European Data Protection Supervisor and the European Commission, has issued guidelines on how to identify the main establishment of a controller or processor under the GDPR3. The guidelines emphasize that the main establishment must reflect the reality of the processing activities and the effective and real exercise of management power over those activities. The guidelines also warn against the practice of “forum shopping”, which occurs when a controller or processor designates its main establishment in a member state with the most flexible or lenient data protection regime, regardless of the actual location of the decision-making or the data processing. The guidelines state that such a practice is forbidden under the GDPR, and that the supervisory authorities will closely monitor and verify the criteria used by the controllers or processors to determine their main establishment. If the supervisory authorities find that the main establishment does not correspond to the factual situation, they may challenge the designation and apply the relevant corrective measures4. References: 1 Art. 4 (16) GDPR – Definitions - General Data Protection Regulation (GDPR)2 Art. 56-58 GDPR – Cooperation and consistency - General Data Protection Regulation (GDPR)3 Guidelines 3/2018 on the territorial scope of the GDPR (Article 3) - European Data Protection Board4 Ibid, p. 14-15.