The encouragement of the accrual of an adequate retirement income has the attention, not only of national governments, but also of the European Commission (EU Member States have initiated reforms of their pension systems, amongst others to provide an adequate pension income. The European Commission stated in 2017 that as part of social protection, every EU citizen should be entitled to an adequate pension, see: European Commission, Commission Recommendation on the European Pillar of Social Rights, C (2017) 2600 final, 26 April 2017, page 8. The European Commission has already expressed this ambition in its White Paper – An Agenda for Adequate, Safe and Sustainable Pensions, published in 2012, see: European Commission, White Paper – An Agenda for Adequate, Safe and Sustainable Pensions, 16 February 2012, COM (2012) 55, page 12. The broadly supported endeavour to achieve an adequate pension income also implies that a multi-pillar approach is recognized by Member States, whereby not only the statutory pension, but also other forms of retirement savings (such as supplementary pension) has to ensure an adequate income after retirement. With regard to promoting cross border labour mobility, reference can be made to the ‘Europe 2020 strategy’.). In cross border situations, a mobile employee may be confronted with various legal obstacles that may hinder an adequate pension accrual and cross border labour mobility. In this article the so-called cross border qualification problems between social security and supplementary pension will be addressed. It is examined how the three qualification problems are recognized in a European law context and to what extent more guidance can be provided on a European level to eliminate the negative consequences of the present qualification problems.