My thesis consists of three essays. Essay one presents a theoretical framework to analyze the optimal choice of exchange rate regimes based on the welfare e ect, and to identify the relationships between trading taxes and exchange rate volatilities. Essay two integrates both the new open economy macroeconomic model and the international real business cycles approach to investigate monetary policy e ects. Essay three explores the real e ects of nominal shocks in a world economy with traded and non-traded goods. The first study develops a simple dynamic general equilibrium framework for assessing the welfare properties of both floating and fixed exchange rate regimes in a two-country, sticky price, and tax distortion model. An important fea...