The Eurozone and the European Union have recently been confronted with a number of existential threats. The sovereign debt crisis and the COVID-19 pandemic have forced European decisionmakers to pass important reforms which have radically transformed the nature and scope of the Union's powers in the field of economic and fiscal policy. As the new economic governance of the Eurozone emerges as the main driver of integration in today's Europe, this book seeks to assess the solidity of the constitutional foundations supporting that system, and its compliance with the Union's core founding value: the rule of law. Using competence allocation, regulatory quality, access to external review and fundamental rights sustainability as analytical benchmarks, this book argues that the recent metamorphosis of Eurozone economic governance has not been accompanied by a parallel strengthening of its constitutional settlement, leading to a problematic misalignment between the Union's action and its governing principles.