European state aid and tax rulings This book investigates whether the European Commission (EC) has the mandate to legislate on direct taxation in sovereign states and ultimately questions whether the ECs enforcement action in recent tax ruling cases in the area of state aid respects the rule of law. [The author] explores whether the ECs recent rulings in relation to member states advanced pricing arrangements reflect a genuine problem of illegal state aid or whether the EC is attempting to use state aid rules to harmonise national tax systems. The author examines this issue through relevant case law comparing the ECs actions with OECD guidance and US practices assessing what is legitimate in terms of the ECs actions and competences. Through the lens of state aid and tax rulings the author addresses the wider constitutional question of how to reconcile national interests with the move towards European harmonisation; does the answer lie in more integration or less Preface Introduction State aid decisions and open formal investigations concerning the tax ruling practices of member states Arms length principle Recovery legitimate expectations and legal certainty EU competences International practices and the OECD The way forward.