Abstract Prior to the international financial crisis, the ECB’s policies were shaped by the interpretation that its mandate was primarily to ensure low inflation. Since the outbreak of the sovereign debt crisis in early 2010, the ECB has adopted a range of policies which have pushed its role well beyond that interpretation. This article presents the argument that ECB policy-making since the start of 2010 undermines the democratic legitimacy of the ECB. The problems stem from three developments: the stretching – and arguably breach – of the ECB’s mandate; the increasing politicization of the ECB’s decisions and policies; and the extent to which the ECB’s policies undermine the transparency of both its own monetary policy and national macroeconomic policies.