The book gathers the general report and the national reports presented at the XXth General Congress of the IACL, in Fukuoka (Japan), on the topic "Debating legal pluralism and constitutionalism: new trajectories for legal theory in the global age". Discussing the major contemporary changes occurring in and problems faced by domestic legal systems in the global age, the book describes how and to what extent these trends affect domestic legal orderings and practices, and challenges the traditional theoretical lenses that are offered to tackle them: constitutionalism and pluralism. Combining comparative law and comparative legal doctrine, and drawing on the national contributions, the general report concludes that most of the classic tools offered by legal doctrine are not appropriate to address most of today's practical and theoretical global legal challenges, and as such, the book also offers new intellectual tools for the global age.