The Amsterdam Call for Open Science invites further exploration of the frontiers of Open Science, suggesting this should be done in particular with regard to data sharing and to methods of opening up the scientific process to society. These suggestions come after a great deal of expertise has been achieved in open access to academic publications. Since the Amsterdam Call, Citizen Science has become a well-established domain in most of the scientific disciplines at the European level, but less is known about Citizen Science practices in the Social Sciences and Humanities (SSH), their specificity and needs, together with the diverse ways SSH researchers carry out for open themselves to participation, making a diversity of publics engaging with their methodologies. Two projects coordinated by OpenEdition Center (EHESS, France), involving SSH researchers and journalists (PLACES project) and more largely other professionals and associations (COESO project) are concrete attempts to address the issues of opening the scientific process to society and to give visibility to the specific SSH Citizen Science practices. They achieve that by encouraging and supporting participatory research and mutual learning between academics and citizens. Furthermore, they built on a major French infrastructure committed to open access to the scientific research in the SSH disciplines. The experiences from PLACES and COESO provide an insight to how open access paves the way for citizen science activities in the social sciences and humanities and how these activities can in turn greatly increase the impact of open access activities. Taking stock of them, it will be possible to highlight some aid and barriers to open participation in knowledge production. Particular attention will be given to the data sharing issue, and to the benefits of mutual learning through participatory research in the rise of scientific literacy. These experiences also provide an overview of the significance that open access and open science infrastructures of services have in supporting citizen science activities.