The current societal transformations, brought by globalization and technological innovation, have disrupted the global and multilevel constitutional landscape, now fragmented in standardized and massified relationships in which inequalities are increasingly amplified. Against such a backdrop, the democratic mechanisms of representation, on the one hand, and the traditional civil law dualistic paths of litigation, on the other hand, appear ineffective in enforcing rights, especially fundamental ones. The present research, theoretical and empirical, aims to evaluate the role of Italian class actions (also referred to, in the European context, as collective or representative actions) as a means of overcoming such challenges and ensuring effective access to justice. Adopting an innovative constitutional-law standpoint, it stems from the recent EU Directive 2020/1828 on representative actions for the protection of the collective interests of consumers, as well as the related national reforms, some of which – like the Italian one – are innovatively trans-substantive. From this, the book analyses, in a broader comparative lens, the constitutional foundations of collective enforcement (as opposed to individual litigation), the specific use of collective proceedings to enforce fundamental rights (rather than mere consumer ones – hence, the originality in the current scholarship context) and the potential drawbacks in light of possible abuse and fair trial guarantees. The topicality of the study is given by the currently developing case law on the matter in all EU Member States, especially in Italy, as well as by the numerous discussions on how to best implement such a tool in a strategic litigation perspective, while upholding essential due process guarantees. The analysis is interdisciplinary, as initially it draws from sociological and socio-legal insights, subsequently theoretically developed and assessed through the aid of case studies. It is also comparative, towards other jurisdictions’ implementation of class actions and towards other more traditional European paths of fundamental rights’ enforcement (e.g. constitutional review and ECtHR applications). The foundational lens, nonetheless, is a constitutional and legal one, since, on the one hand, it does so against the backdrop of the principles of fair trial and effective protection, enshrined under Articles 2, 24 and 111 It. Const., 6 and 13 ECHR, 47 CFREU, and 2 and 19 TEU, as developed by national and supranational Apex courts.