This report was commissioned by the European Commission as part of its Impact Assessment of the proposal for a Common Consolidated Corporate Tax Base (CCCTB) in the European Union. It uses an applied model developed for the purpose that analyses the economies of all 27 EU member states; it models corporate taxes in detail to assess the impact of reform on investment flows, employment, GDP and economic welfare. The research finds that there would be considerable variation in the economic effects of the new tax system on EU countries. The precise estimates depend on the definition of the proposed tax system, but in a typical case, UK GDP would fall slightly, by around 0.05 percent. For other countries the effects on GDP would vary from a rise of 2 percent in Belgium, to a fall of 3 percent in Ireland. Overall, GDP in the EU would also fall slightly, by around 0.15 percent. Capital expenditure would fall a little, by 0.74 percent, but there would be virtually no net effect on employment or wages in the EU.