War has traditionally been understood as an activity carried out by soldiers delivering kinetic energy with weapons on a delimited battlefield. Now, we struggle to define basic concepts such as soldiers, weapons, battlefields, and ultimately, war itself. War has expanded and increasingly given a greater role to non-military means – such as information and cyber warfare, political subversion, and economic statecraft. These are seen to equal, and even surpass, the role of military force. This poses fundamental questions regarding the utility of non-military warfare, the actors involved, and critically how states should act in times defined by non-military warfare. Therefore, this anthology investigates the phenomenon of non-military warfare in different domains, including its relation to military warfare, and how we should think about its utility, its actors, its legality, and how states can understand and counter this activity.