The rules on the conduct of hostilities prescribe the rights and duties of belligerents in their conduct of military operations. Transformations, revolutions and changes of all kinds in armed conflict constantly challenge international humanitarian law. Modern warfare features growing inequality in arms, the emergence of transnational terrorist networks, the privatization of traditional military activities and the near or total collapse of some states. These structural characteristics of warfare today are sometimes beyond the scope of international humanitarian law, but they are also shaking its foundations or having repercussions on the application of certain of its fundamental principles. This issue of the Review illustrates some aspects of present-day methods of warfare and the applicable rules.