Now that it is no longer a taboo to envisage a Greek exit, as well as other countries, from the eurozone, it may be appropriate to revisit the different stages that led to the introduction of the single currency. Prior to the commitment made to that effect in the late 1980s, a currency had begun to be used, albeit modestly, by the countries participating in the European Monetary System, as well as by a few other countries. This private ecu, as it was called, could have become the Community currency that would not have replaced the national currencies, but that would have been available to carry out transactions between two Community member states. This set-up would have been along the lines described by Keynes at the international level at the end of the war. This paper reviews the foundations of the private ecu and how the system functioned. Furthermore, the paper presents an analysis of the role played by the private ecu as it was transformed as the single currency and of he role it could have played by evolving as the common currency of the Community.