The euro is the grandest project in the economic history of Europe. An instrument and an underlying set of institutions, whose success or shortcomings are fundamental to determining the progress of an entire continent. 2019 was the 20th anniversary of the introduction of the euro. Two decades are a sufficiently long period to interpret in economic history terms and to arrive at a deeper understanding and assessment of the lessons from the use of the single currency. There is almost complete agreement about the need for a complete reconsideration of the Maastricht criteria.