By focusing on ECB’s economic policy thinking and its internal politics of ideas, this research aims to provide two contributions to knowledge. Firstly, it seeks to enhance scholarly understanding of ideational change inside international organisations (IOs). To do so, it asks (a) how ECB’s economic policy thinking has evolved since the outbreak of the euro crisis, and (b) what drives change in ECB’s ideas on the best way to deepen Europe’s Economic and Monetary Union (EMU) in its fiscal and economic realms. To answer these questions, fiscal policy, structural reforms and convergence towards resilient economic structures are used as case studies. The article argues that the interplay between changes in ECB’s leadership and internal policy discussions promoted by ideational entrepreneurs played a pivotal role in enabling new ideas to emerge inside the Bank. Secondly, by interrogating ECB’s ideas on the way to complete EMU, this research reflects on the future of the euro. It shares the view that the construction of cognitive authority within IOs is an ongoing political struggle over the ideas underpinning the everyday practice of global governance. By looking at the politics of ideas within the ECB, this article aims to contribute to the international political economy of EMU deepening.