This study is a collection of essays on monetary-fiscal interactions within the European Monetary Union (EMU). Our research focuses on a theoretical evaluation of the Stability and Growth Pact (SGP) and its huge reform debate. The topics chosen are not on the top economists' agenda because the whole field of research has been too young and has not fully been developed, since the beginning of the Monetary Union, in 1999. We analyze the Stability and Growth Pact in new and extended theoretical model frameworks. We ask the following questions on the 'political agenda': 1. What is an optimal fiscal rule in a monetary union? 2. What are internal constraints in a monetary union? 3. Why do larger countries have more problems with the SGP? Our theoretical findings lead us to elaborate a "new" reform proposal on the Stability and Growth Pact. We find a mechanism that allows for a more efficient and credible enforcement of the SGP than in the old and meanwhile reformed Stability Pact. Our aim of providing a comprehensive overview of the fiscal architecture of the EMU is feasible only by means of a close link between methods of economics and political science. This interdisciplinary approach and new field of research supplies a highly promising way of reaching a deeper insight into the present and future interlockings - both on the national as well as the supranational level.