The new intergovernmental science-policy panel (SPP) on chemicals, waste and pollution prevention is currently (2023–2024) being set up. The SPP will need a procedure for defining its work programme and identifying priority topics for its assessments. Possible models for this are the prioritization procedures of the Intergovernmental Panel on Climate Change (IPCC) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). We analyze the priority setting procedures of both intergovernmental bodies, identify some of their strengths and limitations, and provide recommendations for the priority setting procedure of the new SPP. Key finding include: Both IPCC and IPBES separate prioritisation and scoping. Prioritisation means identification and selection of topics for reports; scoping means specifying a report's scope and outlining its content. Both IPCC and IPBES employ procedures that respond to requests by governments, Multilateral Environmental Agreements, and various observers and stakeholders. The procedures are demand-based and offer flexibility and make it possible to reconcile different political perspectives and scientific input. Because a bias towards well-documented and data-rich issues of high visibility is possible in demand-based procedures, it will be important for the new SPP that the function of horizon scanning is connected with the prioritisation procedure.