The competitive pressures arising from European economic integration increasingly challenge the territorial sovereignty of national welfare states. This generates the need to situate domestic social security schemes amid the European Union's national and supranational as well as economic and social spaces. At the trans-national level, the European Commission's 2003 Institutions for Occupational Retirement Provision (IORP) Directive created the illusion that a single market for occupational pensions would shortly be within reach. This did not happen, however, as IORPs — being at one and the same time financial vehicles and social insurance institutions — embody the constitutional asymmetry between policies promoting market efficiency and policies promoting social protection. Whereas the elimination of financial and tax barriers has proceeded smoothly, harmonization of the social and labour components within the occupational pension domain did not occur, slowing down the development of pan-European pension plans. Nonetheless the road towards a single occupational pension market is still open, with first positive results emerging from the greater involvement of corporate and supranational actors.