The ECB started its QE called the PSPP in 2015 as a new monetary policy measure. By purchasing vast monthly amounts of main Member State government bonds, the ECB aimed to force investors towards riskier assets, which in turn, was to increase asset prices and support bank lending, and ultimately lead to growth and inflation. Constitutionally, QE was a new type of complication for the European Macroeconomic Constitution. The ECB became the largest creditor of Member States it was prohibited to finance. The constitutional assessment of the PSPP combines the analysis of the CJEU’s Weiss case that contains very limited constraints for the ECB, and more economic-constitutional and thus substantive analysis. One key question is whether the PSPP is monetary policy, which can be analysed through its objectives, its economic content and examples of other central banks that mostly support an affirmative conclusion. The euro area constitutional structure adds further complications that were also raised in the FCC’s Weiss judgment. The PSPP has arguably broader implications for other areas of economic policy, as it facilitates Member States public finances and increases wealth differences by increasing asset prices, as well as making the ECB deeply dependent on Member States public finances.

The chapter describes and analyses the principles of European Macroeconomic Constitution and how it guides the ECB and EU in its macroeconomic governance. The principles can be divided into objectives and safeguards. The main objective of the economic constitution, integration through internal market, continues but gets price stability as the main macroeconomic objective, and to an extent a more elaborated open market economy principle to guide EU institutions. The safeguards start from central bank independence that are further defined by the prohibition of central bank financing and a narrow central banking model without explicit value judgments. Member States remain responsible for the other areas of economic policy with the obligation of sound fiscal policy. The principles form a logical whole and complement the earlier microeconomic constitution. However, the assumptions and theory backgrounds of the two constitutions differ substantially, which has many implications, including for the role of law and courts as well as independent experts, such as the ECB. These implications have even become apparent already in the earlier case law by the CJEU.

The ECB’s selective bond purchases raised constitutional controversies from the start. The SMP was criticised for overstepping the lines of EU monetary policy and basically financing Member States. The OMT was an effective lender of last resort for governments, although never operationalised. The purchases also gave rise to the first substantive CJEU judgment on monetary policy. The chapter combines economic and legal research to get to the heart of the problems. Specific questions relate to the role of government bonds in the transmission of monetary policy, and to the risks of contagion and currency redenomination as justifiable reasons to selective bond purchases. The broader constitutional assessment of the ECB selective purchases finds many critical areas for the EMU constitutional architecture. Some solutions such as the CJEU's excessive reliance on the objectives of measures for defining them as common monetary policy or Member States economic policy left room for criticism. The chapter argues that the principle of conferral risks becoming void if the independent ECB can effectively dictate its own mandate, calling for a more economic definition of monetary policy. In addition, the circumstances around the programmes raised questions concerning the independence of the ECB.