This PhD thesis examines the political determinants of the policy change of the European Central Bank (ECB) during the euro crisis. The dissertation focuses on the role of economic ideas and strategic action in explaining the decisions of the ECB to activate unconventional monetary policies aimed at preserving financial stability in the 2010-12 period. First, the thesis provides evidence that the failure of policy experiments inspired by ideas of fiscal discipline pushed the ECB to adopt a systemic interpretation of the crisis. This process of ideational change shaped the crisis response of the institution and was influenced by the observation of financial market reactions to different crisis management policies. Second, the thesis documents how the ECB acted strategically to minimise the political risks stemming from uncoordinated policy action in the resolution of the crisis. Taken together, these results shed new light on the politics of central banking in Europe.