The papers in this Special Issue take stock of the functioning of the euro area during its crisis, which encompassed mainly the years 2009–15. They address several questions. For example, what surprises did the euro crisis provide about our knowledge about monetary unions? Why were the interconnections between banking systems and fiscal positions so strong during the euro area crisis? In so doing, they contribute to a deeper understanding of the nature of Europe’s monetary union, the underpinnings of its crisis, and the changes that need to be made to the monetary union so that crises can be prevented in the future.