This article examines the right of Member States to combat abuse, as defined in ECJ case law, in particular, the balance between enforcement of the principle of legal certainty, the right to choose the most favourable fiscal route and the right of states to combat tax avoidance. Part 1 addresses the subjective and objective tests for establishing abuse, the concept of economic reality versus wholly artificial arrangements, the idea of a general principle of community law and the different levels of abuse. Part 2, to be published in European Taxation 7 (2013), analyses, inter alia, how specific an anti-abuse provision should be, the burden of proof, tax jurisdiction shopping and the consequences of abuse.