This paper considers inventors' rights as revealing shifts in the elaboration of public trust in inventions. The two main issues, the method of invention and the credit invested, are analysed both in terms of Diderot's writings and in the economic, social and political context of invention during the eighteenth century. In a pamphlet written in 1755, Histoire et secret de la peinture en cire, Diderot criticized the Count of Caylus's attempt to keep the invention of wax painting secret and to enhance his fame thanks to this technical achievement. Diderot developed a conception of invention as an activity based upon methodical rediscoveries, imitations and translations. Although this could also concern artistic practice, imitation in art had a quite different meaning for Diderot. The main issue was the status of artists and inventors in society. Personal glory and private appropriation were denied to inventors, in contrast to artists. Secrecy, pride and exclusivity in invention were mean and ridiculous strategies. This was precisely what had been happening since the beginning of the eighteenth century, with the development of a market for inventions and exclusive titles, which also affected art. Diderot's narrative of invention as a daily, collective and historical process echoed the necessity of reassessing the value of invention by the criteria of public utility and shared evaluation.