This thesis investigates institutional constraints for social learning in organisational heatwave risk management in London, UK. Empirical evidence stems from 49 semi-structured expert interviews with risk planning officials from London local authorities, health and social care organisations. Findings suggest that the interaction of formal and informal institutions has limited social learning in heatwave planning to incremental changes that reinforced the status-quo. Informal networks and trust relationships between risk managers compensated for formal heatwave planning arrangements that were perceived as dysfunctional. This support from informal institutions to formal strategies undermined opportunities for paradigm shifts in risk planning. It suggests that social learning can be associated with rigidity of established risk management strategies, rather than with their change. In the context of heatwave planning in London, missed opportunities for paradigm shifts concerned a consolidation of reactive risk management approaches that focused on the health implications of heat stress. This consolidation undermined the development of preventive risk management approaches that consider social, environmental and technical risk dimensions. The results of the analysis raise questions about the desirability of learning as an adaptive strategy in the context of climate change. The thesis suggests that learning is not necessarily beneficial for transformation if it is enacted through organisational systems that are inertial and resistant to change.