"The authors have worked on innovation systems for more than a decade. This paper is an attempt to take stock. In section 2 we reflect upon the emergence and fairly rapid diffusion of the concept ‘national system of innovation’ as well as related concepts. In section 3 we describe how the Aalborg version of the concept evolved by a combination of ideas that moved from production structure towards including all elements and relationships contributing to innovation and competence building. In section 4 we discuss the challenges involved both in a theoretical deepening of a fairly narrow version of the concept and in the movement toward the broader approach and in adapting the concept for the analysis of poor countries."