This Working Paper studies the financial and social sustainability of the Belgian social protection system. The results of this publication were presented at the 20st Congrès des économistes belges de langue française and published in the conference proceedings. Assuming no policy changes and against the background of population ageing, the long-term public finance projections highlight an important budgetary challenge. In that framework, this paper examines a number of pathways based on the three pillars of the European strategy as determined during the 2001 Stockholm summit. The budgetary strategy (pillar 1) of the Belgian stability programme in itself does not guarantee the long-term sustainability of public finance and should, therefore, be completed by reforms in support of economic growth (through employment or productivity, pillar 2) or reforms of the pension schemes (as part of pillar 3). The social consequences of the reforms which alter the generosity of the pension schemes should not be overlooked.