Since 2004, risk in the context of nanotechnologies has been criticized as being too abstract and an all-inclusive category. Moreover, the concept of risk is not precise enough to describe the potential issues related to the development of nanotechnologies. Instead, experts on technological development emphasize risk communication. In the field of nanotechnologies, this term was redefined in February 2005 in relation to the question of societal acceptance of nanotechnologies. Risk communication is about gaining stakeholder acceptance of policy decisions, whilst the public and stakeholders are encouraged to participate actively in the communication process through public consultations or hearings. Thus, on the one hand, the category of risk has been pragmatically nuanced to better highlight the vulnerability of the communication of nanotechnologies. On the other hand, this vulnerable communication is not the result of a deficit of information. It is based on the idea of participation, where vulnerability hinges on the social groups specialized in the design, application and diffusion of nanotechnologies within society. How is such participation possible, and what does it entail? We develop this question in the framework of a comparative survey of experts in the development of nanotechnologies in Grenoble (France) and Hamburg (Germany).