Article 107(1) of the Treaty on the Functioning of the European Union [TFEU] declares State aid granted by Member States to be incompatible with the internal market. This principle of incompatibility is not absolute. Under certain conditions, State aid may be exempted from the prohibition of Article 107(1) TFEU. Article 108(3) TFEU requires Member States to inform the European Commission in advance of their plans to grant State aid and the Commission assesses their compatibility with the internal market by examining whether they conform with the conditions for exemption. The Commission is the principal enforcer of the State aid provisions of the Treaty. The supervision carried out by the Commission is supplemented by national courts which also play an important role in the enforcement of State aid rules. They are empowered to apply the prohibition of Article 107(1) TFEU and to take all appropriate action to remedy infringement of Article 108(3) TFEU. Competitors of recipients of State aid that has not been notified to and approved by the Commission can resort to national courts to seek enforcement of the notification obligation imposed by Article 108(3) TFEU on Member States. This “private enforcement” not only supports the “public enforcement” of State aid rules by the Commission, but it also strengthens it by broadening the remedies afforded to competitors of recipients of unlawful aid. For the purposes of this article, “private enforcement” means the initiation of proceedings before national courts for the purpose of seeking compliance with State aid rules. In practice, such proceedings are initiated by competitors of aid recipients. They petition national courts in three separate situations: i) when State aid is granted without prior notification to the European Commission; ii) when State aid that has been found by the Commission to be incompatible with the internal market is not fully recovered as ordered by the Commission; and iii) when they seek compensation for damages caused by unlawful aid.