Health in Humanitarian Crises is a free open-access learning hub covering the major health priorities in emergency and conflict settings, situated within the broader landscape of international health cooperation. It opens with the conceptual and normative foundations of health action -- including universal health coverage, primary health care, social determinants of health, and health system strengthening approaches -- before examining how health systems are analysed and sustained in crises using the WHO six-building-blocks framework. It then addresses the core thematic priorities that define humanitarian health response: sexual and reproductive health, nutrition in emergencies, and infectious diseases. Across these areas, the hub explores the interplay between pre-existing system fragility, acute needs, and the actions of multiple humanitarian actors, and how these can protect or further weaken health systems. It comprises five thematic areas, 35 pages, AI-assisted reflection exercises on each page, and integrated case studies. Designed for humanitarian health practitioners, public health students, and international cooperation professionals, it draws on WHO, UNICEF, UNFPA, and inter-agency frameworks, guidelines, and relevant scientific evidence. Available in English and Spanish at no cost.