This is an introduction to the publication for the first time of a 20-year-old draft paper by Christopher Freeman, the first paper that uses the concept 'national system of innovation'. The draft paper illustrates the role played by Christopher Freeman in building innovation research. This brief introduction gives the status of innovation system discourse and research, and relates it to what Freeman wrote more than 20 years ago. It challenges the idea that 'innovation system is not a theoretical concept', and shows that current innovation system analysis can still learn from Freeman when it comes to linking together trade policy and national innovation systems. Copyright 2004, Oxford University Press.