The provision of safe and sufficient water, sanitation, and hygiene (WASH) services is essential to protecting human health and providing an environment in which people can develop and maintain livelihoods. This is especially true in humanitarian crises, during which safe access to these services is frequently disrupted, often for long periods of time. Humanitarian crises are growing in length and complexity due to external destabilising forces that include the impacts of climate change and ongoing geo-political instabilities. As a result, traditional emergency programming does not effectively address the needs of modern WASH crises. Humanitarian and development WASH professionals must work together in a more coordinated manner to develop effective humanitarian WASH programming that keeps long-term development goals in mind. The authors discuss lessons learned across Africa, Asia, and the Middle East that will inspire humanitarian, development, and other professionals, in and outside the WASH sector, to improve the long-term impact of sustainable WASH programmes in humanitarian contexts. Case studies and conversations with WASH thinkers and programme designers invite readers to reflect on the WASH humanitarian and development divide and reflect on the future of the WASH sector. This book also reflects on how WASH is more than just water service delivery; it is a major contributing factor in facilitating child protection, education, health, and economic recovery. When there is strong inter-sectoral coordination with a strategic, adequate, coherent, and effective response to a humanitarian crisis with a vision for the transition to development, everyone wins.