This PhD-thesis describes the co-evolution of sectoral characteristics, networks of firms and the embedded learning regime from the perspective of a sectoral innovation system (SIS). More specifically, this research aims to shed light on how the institutional environment of a SIS conditions network structures and learning regimes and how outcomes from a learning regime may affect again the institutional environment of a SIS. Moreover, this research aims to understand in how far this co-evolutionary process differs between different SIS’s. In analysing this co-evolutionary process, two views on organisation are combined, namely a competence view and a governance view. Following this, a dynamic model of co-evolution at the level of a SIS is developed based on which a number of hypotheses is developed. To test these hypotheses, two SIS’s in the Netherlands have been studied over the period from the late 1980’s towards the early years of the new millennium : multimedia and pharmaceutical biotechnology. The empirical findings indicate that a general pattern of co-evolution on a sectoral level can be identified. How this pattern settles in network characteristics, coordination mechanisms and in properties of a learning regime is specific to the institutional set-up within a SIS or within different parts of a SIS. In this respect, this study contributes to the understanding of the dynamics of SIS’s as well as of how the optimality of network structure and coordination mechanisms varies with different types of SIS’s ; Victor Gilsing was born in Amstelveen at 18th September 1969. After completing the Gemeentelijk Gymnasium in Hilversum he studied Technology and Business Administration at Twente University from 1987 – 1993. After graduation he started working for Unilever where he held different positions in the field of innovation and business-to-business marketing in the speciality oleochemicals business. From 1998 he worked as a senior policy advisor in the field of innovation policy at the Ministry of Economic Affairs ...