In October 2018 I delivered the Robert Mundell Annual Lecture at the School of Advanced International Studies (SAIS), The John Hopkins University in Bologna. I addressed the connection between the theory of Optimal Currency Areas and the evolution of the euro area by organising my exposition around three questions: 1) What was the role of the OCA theory in influencing the European monetary union initial design; 2) Does the OCA theory help to explain the reasons for the difficulties encountered by the euro area or are other narratives necessary?; 3) and finally, what advice does the theory provide about initiatives to improve the euro area stability and robustness.