This article investigates why the European Central Bank's (ECB's) unconventional monetary policies were relatively modest during the crisis, focusing specifically on the design of its government bond purchase programmes. Building from available explanations of the ECB's behaviour in the political science and public policy literature, we extrapolate a number of testable propositions with a view to helping to account for the specific features of the policies under investigation. These propositions build from scholarly works that emphasize three distinct fundamentals of the ECB's behaviour: legal; doctrinal; and institutional. We then provide evidence supporting our propositions by evaluating the ECB's policy settings during the crisis. In addition, we identify other factors that have shaped the design of the ECB's bond buying policies, namely the ECB's conception of its own independence.