Looking at the historical steps preceeding the planned monetary union, one can see that unification at the economic and political level has always been a primary goal in Europe. Nevertheless, the question of the necessity and the costs of unification should be critically discussed. The aim of this paper is to point out on the basis of empirical facts and theoretical reasoning the advantages and the disadvantages of the monetary union and the economic relevance of the Maastricht criteria. On the one hand, the expected reduction in transaction costs and the increase of the intra-European trade and investment are discussed. On the other hand, the effects which arise by giving up the instruments of an independent monetary policy are considered. I is shown, that the Maastrich criteria alone cannot guarantee an efficient and worldwide competitive European market. The main reason for this is that the latter do not contain aspects of real economic activities, like the overall productivity or the unemployment rate in the different countries, but only monetary criteria. A delay of the monetary union in the current phase, however, would certainly cause serious psycological and economic risks for all national economies in Europe.