On June 5 2012, the Court of Justice of the European Union ruled (Case C-124/10 P) that tax measures may avoid the qualification of State aid if the State acts as a private investor, i.e. if the State’s decision is based on economic evaluations comparable to those which, in the circumstances, a rational private investor in a situation as close as possible to that of the Member State would have had carried out. This complex case can be summarized in one – apparently – simple question: can the European Commission refuse to apply the “Market Economy Investor Principle” to a State measure involving tax prerogatives, because such measures are by nature not available to private investors? The Court answers in the negative and casts a new light on the application of the Market Economy Investor Principle to tax measures. Michel Debroux in Hogan Lovells’ Paris office represents EDF in this complex and lengthy case worth over EUR 1.3 billion and secured a high-profile victory in front the of the Court’s Grand Chamber and against the Advocate General’s opinion, which is rare.