The thesis examines the role of private law and private enforcement in the post crisis EU retail financial markets. Whilst private law and private enforcement have been traditionally regarded as 'foreign bodies' in EU financial regulation, the thesis argues that after the global financial crisis, private law and private enforcement, through courts and alternative dispute resolution (ADR) mechanisms, have become essential tools to compensate retail clients against mis-selling and mitigate systemic risk. To substantiate this argument, the thesis analyzes how the national and EU supervisory authorities, ADRs and courts, in Italy, Spain, France and UK, have interpreted and enforced the EU investor protection regulation (conduct, product and disclosure rules) before and after the global financial crisis. This institutional and comparative analysis shows that the EU regulatory duties, via regulation, 'administrative rule-making', out-of-court dispute resolution and litigation, increasingly influence the interpretation of national private law (Europeanization) and determine its consequent instrumentalization to achieve a high level of investor protection and ensure the stability of the financial market. The thesis argues that this form of instrumentalization has led to the creation of private law remedies and procedures which, albeit based on national law, have become tools to ensure the effective protection of the EU-derived rights (hybridization). After the crisis, the process of hybridization is driven not only by the investor protection objective but also by the financial stability objective which can determine a limitation of the private law law rights and remedies of the investor vis-à-vis the financial firm in order to mitigate the systemic risk, arising, in particular, from vexatious litigation. The thesis discusses the complex relationship between the investor protection and the financial stability objectives of EU financial regulation and examines the extent financial stability concerns can lead to a limitation of the investors rights and remedies in financial disputes.