The research looks at the design of fiscal and monetary policy in EMU. The characteristics of the "economic constitution" established in the Maastricht treaty are analysed to test their robustness to different hypothesis about fiscal sustainability and fiscal and monetary policy interaction. Chapter two illustrates how the possibility of default of public debt in one large member country creates interdependence among fiscal positions of all member countries. Chapter three and four show that a similar kind of interdependence between national fiscal position could be determined by the effect that un-funded fiscal expansions have on the level of prices. The theoretical argument, borrowed from the so called Fiscal Theory of Price Determination, is developed both in a closed economy, to illustrate the basic mechanism and its interpretation, and in a two country monetary union model. Chapter five analyses, in a game theoretical framework, how the interdependence between policy instruments should be recognised in full, in order for any policy to be effective. In a situation in which a possible conflict of objectives or preferences between policy makers is present, any institutional arrangements which does not deal with it positively is intrinsically inefficient and can result in the policies cancelling each other out. The last chapter develops an example on how the conflict between policy institutions can be endogenous to an institutional structure chosen to reduce the influence of policy uncertainty on the economy. It is therefore a note of caution about the common belief that is possible with simple institutional solutions to overcome differences in preferences or objectives that are characteristic of the European environment. The analysis suggests that both greater fiscal policies cooperation and decentralisation of policy institutions from national to regional are developments necessary to achieve the policy goals of the Monetary Union.