Defining disasters and their impacts has several difficulties and limitations due to the complexity of the term. In this chapter, we focus on health disasters, including how disasters impact health systems and how widespread health emergencies can create disasters. A health disaster describes an event that has a direct or indirect negative impact on people’s physical and psychological health. Disasters of all kinds are most impactful to vulnerable groups both in developed and developing countries, and it is important to implement effective disaster risk management to facilitate health systems resilience, mobilising them to resist, withstand and recover from disasters. Barriers and ways in which health systems are resilient are multi-faceted, some of which include financing, human resources, management, infrastructure, access, trust and education. Two case studies illustrate how these barriers have played out in real-world contexts and historical lessons learnt. These include the Chernobyl nuclear and health disaster of 1986 and the 2018 Ebola outbreak in the Democratic Republic of Congo. This chapter identifies four priorities for action: understand risk, strengthen governance, invest in resilience and enhance preparedness and considers these on all levels from international to individual. Hazards themselves will not cause health disasters but instead how society reacts and the barriers to resilience. By moving health system resilience to the forefront of legislation and governance, disasters can be mitigated and promote sustainable development throughout the world.