This book provides clear guidance on what constitutes State Aid in the area of tax law. It clearly explains the situations in which beneficial tax provisions for the taxpayer - e.g., lower tax rates for certain industries or for certain economic zones, advantageous depreciation rules, or exemptions - can be declared void by the European Commission. The difficult controlling concept of ‘selectivity’ of an aid is dealt with extensively. Drawing on familiarity with the practice of the Commission, as well as the jurisprudence of the General Court and of the Court of Justice, thirteen knowledgeable contributors present valuable arguments in case the Commission requires the repayment of advantages received. Among the topics and issues covered are the following: how unregulated tax incentive competition between States leads to a ‘win’ by one State and a ‘loss’ by another; the legal uncertainty attached to the Commission’s decision following notification of a proposed tax incentive; the role of the Commission’s Code of Conduct; calculating the amount of recovery of illegal State Aid; application of State Aid rules in the area of indirect taxation (e.g., VAT and excise duties); investment fund regimes; subnational regional aid; ‘patent box’ regimes; foreign source income; and taxpayers’ exclusion from infringement proceedings and subsequent appeals.