We speculate about how Europe's monetary union will evolve in the next five to ten years. We concentrate on what is likely to be the most important change in that period, namely, the increased number and heterogeneity of the participating states. New members will be sharply different from the incumbents in terms of their per capita incomes and economic structures. We concentrate on the implications of this development for the structure, organization and operation of the monetary union. We focus on the implications for the conduct of monetary policy of voting and representation rules on the ECB Board on the grounds that these will have to change with the accession of additional members. We focus on prudential supervision and lending in the last resort on the grounds that the inclusion of countries with recently-created and still-developing financial systems will be among the most prominent consequences of EMU enlargement. We focus on the coordination of fiscal policies on the grounds that the fiscal positions and problems of the accession economies will differ from those of the incumbents. And we focus on labor market flexibility on the grounds that labor-market effects will be among the leading consequences of the admission of new members.