The fourth volume of the proceedings of the XXIX FIDE Congress in The Hague in 2020. The proceedings of the XXIX FIDE Congress in The Hague are published in four volumes. The first three volumes were published in 2020. This book (Vol. 4) contains the congress proceedings of the XXIXth FIDE congress that, after years of preparation and the disruption caused by COVID-19, could finally take place in The Hague. 1 Introduction; 2 Congress Programme; 3 Topic 1: The Pivotal Role of National Courts in the EU Legal Order; 3.1 Rapporteurs (General, Institutional and National); 3.2 Update General Report; 3.3 Updates National Reports; 3.4 Report to the Plenary; 4 Topic 2: The New EU Data Protection Regime; 4.1 Rapporteurs (General, Institutional and National); 4.2 Update General and Institutional Reports; 4.3 Updates National Reports; 4.4 Report to the Plenary; 5 Topic 3: EU Competition Law and the Digital Economy; 5.1 Rapporteurs (Institutional, General and National); 5.2 Update General Report; 5.3 Update Institutional Report; 5.4 Updates National Reports; 5.5 Report to the Plenary; 6 Reports on Panel Discussions; 6.1 Fit for the Future: What Role for Europe at Home and in the World?; 6.2 The Role of Courts in Upholding the EU’s Foundational Values in Article 2 TEU; 7 Speeches; 7.1 Welcome Address by the President of FIDE XXIX; 7.2 Speech by the President of the Court of Justice of the European Union; 7.3 Speech by the President of the General Court; 7.4 Speech by the President of the Supreme Court of the Netherlands; 7.5 Speech by the President of the UK Association for European Law; 7.6 Speech by the Executive Vice-President of the European Commission; 7.7 Speech by the Mayor of The Hague; 7.8 Speech by the Minister for Foreign Trade and Development Cooperation; 7.9 Speech by the European Chief Prosecutor; 8 The XXX FIDE Congress in Sofia, Bulgaria (31 May-2 June 2023)