Assessing impact, sharing control: analyzing multi-stakeholder relationships in open science infrastructures Open science platforms are a new type of meeting point between scientific offer and scientific demand. They increase (1) the variety of available scientific resources (journal articles, educational toolkits, raw and processed data, software, research notebooks), (2) their findability, accessibility, interoperability and reusability and (3) the variety of possible usages and users of those resources (especially societal and economical). These changes are both causing, and caused by, the recomposition of the stakeholders either contributing to, using, operating, financing and regulating those infrastructures, in a way unheard in previous knowledge regimes: governments, research funding organizations (RFOs), industry, publishers, research producing organizations (RPOs), research communities, civil societies and general public. Proper impact assessment of open science policies is thus required to (1) better understand the academic, economical and societal effects those platforms and other open data commons have, (2) figure out whether the actual impact is indeed in line with the promoted and desired objectives (3) base future public policies on these evidences. But impact assessment does only indirectly address the question of infrastructure control, especially the issue of disparities between big-scale and grassroots actors, that especially shows in so called “citizen science” and the possible solutions to mitigate power imbalances, especially by using law as an incentive. We will discuss those questions by presenting the latest findings and research questions of two EU funded projects hosted at CIS: the Odeco open data project and the PathOS open science project.