This guide provides strategic direction for host countries, event organizers, health authorities, and key stakeholders to effectively plan and conduct Simulation Exercises (SimEx) and After Action Reviews (AARs) for mass gathering events. Packed with practical tools, it empowers users to seamlessly integrate these activities into ongoing learning and emergency risk management processes. Aligned with the International Health Regulations (IHR, 2005), the guide serves as a critical resource for strengthening global and national health resilience, ensuring safer and more prepared mass gatherings.