First of all, the irrevocable fixing of exchange rates between the participating currencies and the introduction of the euro on 1 January 1999 can rightly be considered as the "crowning" of the Single Market. The euro is indeed "One money for one market", as the studies supporting the original Delors Report succinctly put it.
The euro has undoubtedly become an important catalyst in promoting the further integration of product and capital markets of euro area economies. More importantly, the policy-makers in the Member States have realised that being part of a monetary union will not only produce substantial economic benefits. It also imposes certain constraints on their own policies.