This article describes the historical evolution which led to the creation of the Euro. It presents the reasons why a single currency has been launched in Europe and it analyses the consequences of the Euro in two fields : the implementation of macroeconomic policies and the working of the international monetary system. The conclusion of the article is that the monetary organization in Europe is unbalanced and has not been completed. This conclusion raises the crucial problem of the governance of the Euro zone. – Summary AFRI-2002