Transfusion emergency preparedness is increasingly being recognized as an important element in the healthcare response to mass casualty events (MCE). Planning should be designed to support an integrated response between the blood services and hospitals. The lessons identified from the Manchester Arena bombing in 2017 and recent incidents in London have led to new guidance. Demand planning has been informed by the global experience of civilian MCEs and the changing trends in trauma care. Past evidence suggests that only a modest number of hospitalized patients following MCEs require transfusion. The mean blood use per patient admitted is consistently calculated at 2–3 red cell units. Most blood is used within the first 6 h. However, a small number of critically injured with multi‐trauma may require massive transfusion and ongoing support. Many blood services have reported meeting the initial overall demand for blood from stock. However, universal components may be in short supply. The demand can be managed by pre‐agreed substitutions. Early transfusion triage enables the best use of hospital laboratory and blood service support. Careful communication with donor communities is essential to manage a controlled replenishment of stocks. Future challenges for the transfusion community include the trend towards lower red cell stock holdings and the changing trends in weapon use and tactics. A standardized approach to transfusion data collection is required to support future planning. The transfusion community is encouraged to plan for MCEs, contribute to ‘after action reviews’ and work together for safe and sustainable transfusion support.