In this thoroughly updated second edition of what has quickly become the definitive text in the field of international humanitarian law (IHL), leading expert Marco Sassòli evaluates the application of IHL, the way in which hostilities should be conducted against an adversary, and the pertinence of traditional distinctions, such as that between international and non-international armed conflicts or civilians and combatants. Drawing on the author's practical experience to provide unique and invaluable insights, the second edition discusses the rules protecting certain categories of persons, including prisoners of war, as well as governing different types of conduct of hostilities and the difficulties in determining whether a destruction was unlawful. Significantly, the edition takes the armed conflict between Russia and Ukraine into account, discussing what remains of neutrality, defending the strict separation between the prohibition of aggression and the humanitarian rules to be respected by both sides, which must however be nuanced in the field of naval warfare. New sections explore IHL in relation to persons with disabilities, sieges and humanitarian corridors, the role of the media, IHL in outer space, and the concept of meaningful human control over lethal autonomous weapons systems. Structured in a clear and accessible manner, this new edition is essential reading for all students and scholars of international humanitarian law, as well as those in human rights, and public international law. For military practitioners and NGO lawyers, as well as those working in intergovernmental organizations, this is simply a must-have resource.