This open access book establishes an interpretative framework by means of a functionalist-originalist reading of EU law and comparative federalism, in particular US constitutional law. The EU is undergoing one of the most profound structural crises of its history, relating to the rule of law and fundamental rights. The author conceptualises the existential question in terms of ontology, constitutional legitimacy, doctrine and institutional process. By providing the first conceptual methodology (based on comparative federalism and focusing on law and rights) the book develops proposals which can be used to address the EU's current constitutional challenges. The ebook editions of this book are available open access under a CC BY-NC-ND 4.0 licence on bloomsburycollections.com.