The Court of Justice has been alluding to 'abuse and abusive practices' for more than thirty years, but for a long time the significance of these references has been unclear. Few lawyers examined the case law, and those who did doubted whether it had led to the development of a legal principle. Within the last few years there has been a radical change of attitude, largely due to the development by the Court of an abuse test and its application within the field of taxation. In this book, academics and practitioners from all over Europe discuss the development of the Court's approach to abuse of law across the whole spectrum of European Union law, analysing the case-law from the 1970s to the present day and exploring the consequences of the introduction of the newly designated 'principle of prohibition of abuse of law' for the development of the laws of the EU and those of the Member States.