The chapter analyses how the ECB was granted responsibility over prudential supervision as part of the EU banking union. This changed the EU perspective on financial services from internal market issue to a macroeconomic financial stability issue. The ECB now supervises directly the largest banking groups in the euro area and monitors the supervision of all other banks as well. The ECB’s role in the banking union raises new types of constitutional questions and requires a different analytical framework. A formal legal assessment, particularly on the legal basis for conferring specific tasks on the ECB under Article 127(6) TFEU, is complemented with a broader economic constitutional analysis. Here, the context in which the banking union was initiated is particularly important. The chapter also discusses the merits and caveats of combining banking supervision and monetary policy, where the conflict of interest is the main caveat particularly for an independent institution such as the ECB. It is also concluded that the supervision could return to the internal market setting and again be separated from monetary policy in the future.

Not only the member states should be given credit for the survival of the single currency. The European Central Bank deserves credit too. Throughout the crisis it resorted to ‘unconventional’ measures that have proven crucial for the stability of the currency union, especially its government bond programmes SMP and OMT. This chapter examines these programmes and argues that they are an intrinsic part of the transformation of the euro. Since the Bank’s mandate and constitutional position ultimately rest on the Founding Contract between the member states, it could not intervene in bond markets without a prior change in this Contract through which states committed themselves to a different currency union based on a broader stability conception. Only such a contractual change, and confirmation of it through concrete action, could provide the necessary political cover for bond purchases that pushed the boundaries of the Bank’s original mandate.