Citizens’ assemblies on climate change are increasingly popular to support democratic decision-making. Such Climate Assemblies (CAs) convene representative groups of citizens formulating policy proposals after hearing experts and deliberating intensely. CAs may help addressing climate policy issues more effectively partly because their members need not worry about re-election. CAs’ effectiveness depends on their design such as the issues chosen (or not chosen) for deliberation. Agenda-setters exert substantial power by selecting certain issues and by choosing framings that benefit some solutions over others. In this paper I ask: What characterizes agendas that are suitable and legitimate for deliberation in CAs? The aim is to support practitioners in making informed agenda choices for CAs by providing a list of ten widely accepted guiding principles based on expert interviews, policy documents, and information gathered from the Knowledge Network on Climate Assemblies (KNOCA). The paper systematically discusses trade-offs of various agenda choices in the light of different CA rationales. Results show that those with system-supporting rationales tend to favour narrower agendas tailored to political demands aiming to increase immediate policy impact; those with system-disrupting rationales prefer more open agendas allowing citizens to challenge existing political practices and worldviews. Results support earlier arguments that distinctions of entire deliberative processes in either top-down or bottom-up are too simplistic and that a tool-box approach is more useful. Insights appear relevant for debates of deliberative minipublics more generally. Future research should investigate whom to involve in setting CA agendas and with how much power.