Income differentials between the qualified and unqualified which have increased in the last two decades are explained by the increasing importance of international trade (outsourcing of wage-intensive production processes to low-wage countries) or skill biased technical change (technical progress which favours the qualified and highly qualified). As yet theoretical and empirical research into the subject concentrates mainly on the demand side, that is to say the labour demand change (substitution of unqualified with qualified staff) of companies due to technical progress or (in countries with low-wage economies) outsourced processes. Within the framework of the project this gap shall be closed by integration of the supply side into an aggregate model on the one hand and by detailed analyses of the further education behaviour of private sector enterprises on the other. All analyses are based on comparable data of European countries. The empirical research of the ZEW project team is mainly based on data from the Mannheim Innovation Panels.