In this chapter, the authors use actor-network theory (ANT) to explore the relations between uncertainties in co-design processes and the quality of participation. To do so, the authors investigate Latour's discussion uncertainties in relation to social processes: the nature of actors, actions, objects, facts/matters of concern, and the study of the social. To engage with the discussion on uncertainties in co-design and, more specific in infrastructuring, this chapter clusters the diversity of articulations of the role and place of uncertainty in co-design into four uncertainty models: (1) the neoliberal, (2) the management, (3) the disruptive, and (4) the open uncertainty model. To deepen the reflections on the latter, the authors evaluate the relations between the role and place of uncertainty in two infrastructuring processes in the domain of healthcare and the quality of these processes. In the final reflections, the authors elaborate on how ANT supported in developing a “lens” to assess how uncertainties hinder or contribute to the quality of participation.