Following the Great Financial Crisis, the European Central Bank's functions have been significantly altered. It is now involved in the functioning of a variety of European Union bodies and agencies, new powers in the field of banking supervision have been attributed to it and it has resorted to unconventional monetary policy. Such a concentration of powers arguably gives rise to issues of accountability and institutional balance within the European Union: (i) the resulting institutional framework is particularly complex and difficult to understand; (ii) the numerous functions the European Central Bank assumes makes it increasingly difficult to identify in which arena(s) it should be held to account for which action; and (iii) its role in the different bodies or agencies may vary in theory and in practice, which, in turn, influences the degree to which the European Central Bank should be held to account. This article aims at showing to what extent the European Central Bank's role has multiplied and diversified with a view to assess how it is held to account in those different instances, and what the consequences are for the European Central Bank's democratic accountability, primarily towards the European Parliament, as well as towards the Council of the European Union and national parliaments where applicable.