This paper analyzes how the IPCC understands and addresses with risk and uncertainty. First, it discusses the IPCC’s formal and explicit view on how it understands, manages, and communicates risk and uncertainty in its knowledge assessments. This is done through an analysis of the documents that the IPCC has produced on the subject. The analysis reveals that the IPCC has an ambitious yet complicated system for identifying, assessing, and managing risk and uncertainty. The paper then explores how IPCC experts – researchers appointed by the IPCC to conduct its knowledge assessments – view this system and use it to determine risk and uncertainty. This is done through an interview study with IPCC experts. The analysis indicates that there are tensions in the way knowledge, uncertainty, and risk are viewed. Interviewees made limited reference to the IPCC’s formalized view of risk and uncertainty, but based on the little they did say, it appears to help them manage not only risk and uncertainty, but also internal disagreements and divergent research traditions. Finally, the paper draws conclusions about the challenges that the IPCC will face and need to address regarding risk and uncertainty.