Openness of knowledge was in the Dutch Republic no more a natural state of affairs than in other parts of Europe at the time, but it became dominant there at an earlier date than elsewhere. This puzzling phenomenon is the subject of this essay. The article shows that tendencies to secrecy in crafts and trades in the Netherlands were by no means absent and that public authorities were not principled supporters of openness. Openness of knowledge did not prevail because arguments in favour of a free exchange of knowledge won the day against a rhetoric in defense of secrecy or because a rapid change in methods of production and marketing rendered the maintenance of craft secrecy practically impossible. The weakness of secrecy in the early-modern Netherlands, this essay argues, can be explained by the relative tardiness of the growth of the corporate system and the typical features of the institutional structure of the Dutch Republic. Craft secrecy in the Dutch Republic, as far as it existed before the middle of the eighteenth century, was normally based on a contractual relationship between individual actors rather than on any form of enforcement by public agencies.