This book bridges the study of European constitutionalism with the study of 'fiscal federalism' - the subfield of public economics concerned with structuring public finances between different levels of government in federal states. On one axis, this book delves into European Union and Member State constitutional law from all EU Member States in order to investigate and identify the existence of permanent constitutional boundaries that will impinge upon the selection of proposed models for EU fiscal federalism. On the second axis, this book engages the study of fiscal federalism in order to determine which institutional configurations known to that field remain legally and economically implementable within those boundaries. It provides a far-reaching investigation of which models of fiscal federalism are compatible with the constitutional boundaries of the European legal order.