At the beginning of the 20th century, the discovery of quantum mechanics put into question the understanding of the world has dominated by necessity that had characterized classical mechanics. But, was it the first time in which nature was seen as contingent? Was necessity always at the core of every scientific understanding of the world? Focusing on Renaissance and early modern science, my project argues that a vision of the world as dominated by necessity emerged only in the seventeenth century, and slowly and contradictorily, from a previous understanding of nature as the »realm of contingency«.