the treaty because only 5 member states were ready to implement them at the time. second example is the social charter, that was negotiated together with the maastricht treaty, but that was not acceptable at the time for the british government. a third example of flexibility brings me back to my own business. as you surely know only 12 out of the 15 current member states have until now adopted the single currency. according to the treaty, member states that have not yet adopted the euro are called " member states with a derogation ". two categories can be distinguished. the uk and denmark make up one category : these member states got respectively an opt - in and an opt - out. the second category consists of the member states that can't adopt the euro because they do not yet comply with the well - known convergence criteria. only sweden is currently in this position, but very soon a number of new member states will join sweden, having the vocation - and even the legal obligation - to adopt the euro at the right moment. it is very obvious that the member states of the euro area are more advanced in economic integration than the others are. so, this is clearly a case of " closer co - operation ", which has taken shape in the creation of a forum where the ecofin - ministers of the euro area can discuss the economic situation in the world, in the european community and in the euro area, and its consequences for economic policy making. this forum is, as you know, called the " eurogroup " and i'm sure that minister reynders will tell you everything about it after lunch. so to us, central bankers, closer co - operation or models of flexible integration is not some kind of theoretical exercise, we live with it constantly. ladies and gentlemen, my feeling is that the royal institute and the national bank have chosen for the colloquium of today a topic that is very much alive in the ongoing debate about the future institutional framework of european integration. the fact that we could find a series of utmost distinguished speakers ready to discuss this topic today with you, is a further demonstration of its importance.

integration and stability are highly correlated and we believe that this applies not only to monetary policy but also to for instance foreign policy. our trust in european integration is one of the reasons why we at the national bank of belgium are very happy that we got the opportunity to organise the colloquium of today in close co - operation with the royal institute for international relations. a second reason is that we feel like naturally related to the european construction. belgium is indeed one of the six founding fathers of the european union and brussels hosts the main headquarters of the european institutions. at several occasions the national bank of belgium provided the link between the european central banks and the european institutions, for instance on the 31st of december 1998, when the ecofin - ministers met in the consilium building in order to fix the irrevocable conversion rates of the euro. it can't be surprising that we are - maybe more than our colleagues are - keen on the institutional aspects of the european integration. today's colloquium is set against the background of the european convention and the imminent enlargement of the union. the topic we would like to discuss today is the controversial idea of flexibility. is it right that we need more flexibility than provided for by the nice treaty, if we want the larger and more heterogeneous union to function effectively? in the very near future we will indeed be confronted with two challenges when it comes to european integration. one is that the eu is going to expand to an important extent. next year the number of citizens in the eu will increase by 20 %. second challenge is that part of the member states want to deepen the integration, but probably only part of them! i am surely not against the establishment of a larger free trade zone in europe, in particular as a central bank governor. but, as a citizen, my ambition for europe is higher. what instruments do we need to be able to reconcile expansion and deepening? can i recall to you that the former belgian prime - minister leo tindemans argued already in 1975 - more than a quarter of a century ago - in his " report on the european union " in favour of flexibility as a means of deepening the integration process, particularly for monetary policy. it seems that there is nothing new under the sun. and indeed, models of flexible co - operation have already been used in european integration in the past. we can think of the schengen accords agreed in 1985 but originally kept outside