The open science policy synthetises the best practices in the scientific knowledge system and draws a trait d’union between the law, science, technology and society. With the 2021 UNESCO Recommendation on Open Science, the latter has been elevated to a global institutional public policy and a living co-regulatory process of science governance. Open practices of scientific knowledge co-production, collaboration, evaluation and circulation have become the global standards stemming from social needs and facts and spelled out in values, principles and lines of action. A soft law framework has emerged from below, notably from the factual genesis and normativity of socio-technological practices enabled by Web 2.0 and 3.0. This article traces the birth and evolution of open science practices from the illegal or ultra-legal roots in the shadow libraries and the coeval open culture/access bottom-up movement through the self-regulating scientific commons until today’s multi-level co-regulatory and participatory model of global institutional governance of science. Finally, it prefigures the birth of a global law of science (lex scientiae).