There is a growing consensus that something is amiss with the European Monetary Union (EMU), although there is no agreement as to what exactly the problem is. The explanation is to be found in the EMU's constitutional circumstances. A monetary union without a political union contains a built-in source of weakness. The fact that the European Central Bank has no effective counterpart in a European government creates a vacuum around it, which is felt by markets and affects the bank's ability to assert true leadership. This constitutional and political weakness is at the heart of the euro's problems; yet it has been systematically side-stepped in the long run-up to the Maastricht Treaty and its implementation. The EMU will remain structurally weak as long as this imbalance between monetary and political union persists, and could even become the trigger for a serious European and international crisis.