The European Commission has received a mandate from the Council for a study on taxation in the EU. This study should illuminate, among other things and taking into account the results of the Ruding-Report (1992), existing differences in effective levels of corporate taxation in the EU. Based on the methodological approach of Devereux and Griffith this study presents estimates both of the effective marginal and effective average tax rates on investments in the Member States. The base case considers domestic and cross-border investments and primarily corporation taxes in each country, but also includes analysis of personal taxes on investment and saving. The main aim of the analysis is to compare effective tax rates on economic activity in different locations within the EU. A secondary aim is to analyse differences in effective tax rates between different types on investment. Besides the base case scenario the taxation of small and medium sized enterprises (SME), the effects of tax optimisation strategies in the field of intra-group financing and the consequences of tax harmonisation scenarios have been considered in various sensitivity analysis and simulations.