This chapter looks at the evolution of the legal framework for State aid during the past six decades of economic integration and addresses State aid rules in the context of balancing national policy objectives with the necessity to review aids at a supranational level. A dual trend emerges from the evolution of State aid rules over the last sixty years. On the one hand, the Court of Justice has played a key role in establishing new principles and designing rules governing State aid. In parallel, the Commission also acts as a rule-maker, by introducing relevant soft law and regulatory texts. In this context, the adoption of the Procedural Regulation in 1999 can be regarded as a turning point in the codification and development of State aid rules. The development of State aid is, however, not completed, as reflected in the last reforms of the State Aid Action Plan and the State Aid Modernization initiative.