This article explores the evolving concept of competition within the framework of European Union law, focusing particularly on how interpretations of antitrust law have shifted over time as a consequence of the level of achievement of the single European market. The more the single European market was created, the more antitrust law moved away from the rigid prohibition of compartmentalizing markets on a national basis and opened up to an interpretation that was more attentive to the needs of economic efficiency. The enlargement of the EU to include new member States poses challenges similar to those faced by European antitrust in the 1960s and is likely to allow EU competition law to consider market integration goals prevalent over strict economic efficiencies.