"Social Europe" has been constructed following 50 years of EEC and EU policy-making, which has gradually extricated social questions from a pure rationale of economic integration in order to turn it into a lever for European political integration. The theoretical and disciplinary viewpoints are presented that, together, help us better understand the processes at work. Attention is drawn to three of them. First of all, the evolutionary process of building the EU accounts both for the differences between social Europe and national welfare systems, and for an ongoing process of institutional creation through an accumulation of EU legal achievements (acquis). Secondly, the expansion of the EU to twelve new member states lacking robust labor rel...