The current times of constitutional transformation in the EU place the following question on the agenda: Is the ongoing economic crisis demarcating the end of the original conception of a 'European Economic Constitution' as it has developed since the early days of the EEC? Or are we witnessing simply a shift towards a new more encompassing model of an EU 'Economic Constitution' in which economic government and economic governance tools are used in parallel to deepen integration and continue the spill-over of economic integration into previously national policies? This contribution traces and evaluates conceptual, regulatory, institutional and legitimacy-related changes and challenges to the EU's model of the 'Economic Constitution' as the basic EU legal framework governing economic policy. This chapter argues that the EU's constitutional framework in the form of the existing Treaties and General Principles of EU law did not provide an adequate legal framework to cope with the ongoing crisis. This failure has, in our view, initiated an ongoing transformation of the EU's 'Economic Constitution' as we know it. Laying the foundations for the transformation took place in several consecutive steps mostly on the intergovernmental level and often as a combination of EU law, public international law and in some cases mixed with private law instruments. The nature of this evolution creates challenges with regard to ensuring compliance of these newly developed structures with the Union's foundational principles of ensuring transparency, democratic legitimacy, fundamental rights and effective review mechanisms in the context of a system under the rule of law. In order to illustrate the modes of the continuous transformation of the 'Economic Constitution' and to evaluate the direction it is taking, this chapter will start with tracing its origins and follow its evolution over time. It thereby distinguishes two separate but interlinked elements of the 'Economic Constitution.' It first looks at the original focus of European regulation regarding what we refer to as 'micro-economic' matters with policies including competition law and the control of state aids. This chapter then turns to the evolving focus of EU law the larger questions of economic and fiscal policies which we refer to in the following as the 'macro-economic' element of the constitutional framework.