Part 1 of this paper (published in the previous issue) documented comparative case law in a number of areas - from the single market to the Data Retention Directive, European Arrest Warrant, ESM Treaty and constitutional review - where constitutional rights and rule of law safeguards have been levelled downwards in the context of implementation of EU law in different Member States. Here, Part 2 of the paper propounds the concept of ‘substantive co-operative constitutionalism’, exploring how European constitutional law and the European constitutional law discourse could be recalibrated towards a greater responsiveness to substantive constitutional values. Part 2 starts by outlining an increasing shift from the mindset and vocabulary of classic, comparative (continental) European constitutional law, to a more formal, procedural, thin version of EU constitutionalism, where the keywords are supremacy, uniformity, direct effect, autonomy, effectiveness and trust. Indeed in the context of democracy and legitimacy in transnational governance, some scholars have written about the ‘erosion’, ‘twilight’ or ‘decline’ of constitutionalism or ‘the end of constitutionalism as we know it’. More recently, Euro crisis measures have prompted heightened concerns about the prolonged and perhaps even irreversible suspension of constitutionalism, the Rechtsstaat and democracy. Yet in the mainstream EU and transnational constitutional law discourse, such concerns have generally received limited attention. The article traces the reasons for the shift in the paradigm of constitutionalism on the basis of the literature on the epistemology of EU law and of transnational constitutional law, and argues that such a shift is not the only way forward. The paper then proceeds to outline some suggestions on how a more substantive version of co-operative constitutionalism could be operationalised in practice. This includes a significantly more probing and proactive role for the national constitutional courts, supreme courts and national parliaments, as well as the creation of mechanisms in the EU institutional and judicial framework for greater responsiveness to constitutional values and constitutional diversity.