We often think of Tokugawa Japan as a closed society. As represented by Hiraga Gennai - one of the most colourfully inventive figures of his age - we see that domestic and imported knowledge and skill were put to work there in carefully managed ways to achieve domestic peace and prosperity. Gennai's career has much to tell us about how material and knowledge production went hand-in-hand in Tokugawa Japan and the extent to which local interests directed the adoption and adaptation of European knowledge and skills. Tracing his biography reveals that the analytical distinctions so often made between science, technology and commerce do not hold up in practice and should also serve as a warning against histories of the global 'diffusion' or 'influence' of western science.