Book excerpt: This book is a compilation of contributions exploring the impact of the European Treaty provisions regarding state aid on Member States’ legislation and administrative practice in the area of business taxation. Starting from a detailed analysis of the European Courts’ jurisprudence on Art.107 TFEU the authors lay out fundamental issues – e.g. on legal concepts like “advantage”, “selectivity” and “discrimination” – and explore current problems – in particular policy and practice regarding “harmful” tax competition within the European Union. This includes the Member States’ Code of Conduct on business taxation, the limits to anti-avoidance legislation and the options for legislation on patent boxes. The European Commission’s recent findings on preferential “rulings” are discussed as well as the general relationship between international tax law, transfer pricing standards and the European prohibition on selective fiscal aids.