This purpose of this pedagogic resource is to offer an overview for uncertainty assessment relating to complex science-policy problems. We propose that tools to assess uncertainty must take into account three types of concerns. The first concern is the identification and the analysis of the various forms of uncertainty that stakeholders and decision maker have to face. The second concern is linked to the quality of knowledge and its evaluation by the scientific community and/or an extended community of peers. The third concern is the pertinence and “fitness for purpose” of our knowledge, including knowledge about uncertainties, in a given decision, policy or governance context. We therefore consider, in the paper, topics related to characterization of uncertainty, to the complementarity of of analytical and deliberative methods in the evaluation of the quality of knowledge, and to deliberation support tools intended to facilitate communication, structuring, and framing of knowledge in different sociocultural and political contexts.