It is well established that continuous development of local-level mitigation policy plans and actions increases the chances of effective responses to natural hazards. What is less well known is how and why policy development, including the scope and pace of changes in municipality crisis mitigation programs, varies across local-level crisis mitigation systems. Using survey data on municipality hazard mitigation policy in Sweden, this study documents patterns of policy development and explores candidate explanations. Special attention is devoted to floods, which present local managers with opportunities to learn and adjust local mitigation policies. To investigate floods along with other hazards as potential drivers for local mitigation policy, the study examines three approaches to policy development: external shocks, transformation without disruption, and regional diffusion. Overall, in this case, the transformation without disruption model and the regional diffusion model do better than the external shocks model. Important precursors of policy development include collaboration, learning and diffusion effects from events and policy adoption in nearby municipalities. The study demonstrates the value of a broader analytical approach to policy development, which takes into account the interplay between events, collaborative management, and learning.