The International Platform for Biodiversity and Ecosystem Services (IPBES) was launched in 2012. Its objective is to strengthen the science-policy interface for the conservation and sustainable use of biodiversity, long-term human well-being, and sustainable development. Nonstate Actors (NSAs) participated in the inception of the platform and are also assumed to play a key role in its coming assessments and reports. In order to encourage NSAs to participate and self-organize, an institutional process has been led by the Secretariat in collaboration with two main organizations: Diversitas-International Council for Science (ICSU) and the International Union for Conservation of Nature (IUCN). We look at the construction of this stakeholder participation process and its effectiveness. To what degree is the stakeholder engagement effective and what are the different forms of involvement? What methods are used by the IPBES's Secretariat and its mandated organizations to encourage stakeholder participation in the Platform? A social network analysis survey revealed four categories of actors in the group of stakeholders: organizers, connected, closely-knit, and peripheral. The ethnographic approach analyzed the way in which the IPBES secretariat organized the stakeholders' days, managed them, and controlled them. Thanks to these two methods, we analyzed the relational structure of the group of stakeholders and their contours of involvement and showed that these two dimensions can combine in a different way. The idea of a group of stakeholders, promoted by IPBES, is accompanied by a leadership/participation model that tends to enroll the stakeholders involved but may conversely marginalize some dissenting voices.