Eradicating and addressing child marriage in situations of armed conflict requires that stakeholders increase their attention, knowledge, evidence-based protection measures, and resources in a coordinated fashion. To this end, this article examines what constitutes child marriage within the international legal framework. It then presents a concise analysis of what is known about child marriage in development contexts, before moving on to discuss the (limited) state of knowledge on child marriage in humanitarian settings, and the global response. It presents information on different married child populations, including child brides and grooms, girls forcibly married to armed actors, child widows, and child marriage within natural disasters. It concludes with ideas on the information and knowledge that is still needed to inform effective response.