The governance of war is the focus of multiple interventions by different international organizations and is manifest in multiple mechanisms and at multiple levels. A long historical perspective renders visible the “laws of armed conflict,” standards of international humanitarian law that govern conduct during war, as part of these mechanisms. A more contemporary view, by contrast, makes apparent not only the various ways that conceptions of war have changed over time, but also expectations about its governance and the relationship of war governance to conflict prevention, conflict resolution, and post-conflict governance. This chapter engages briefly with questions about what war is, by whom wars are fought, and with what effects, as a prelude to an examination of how war is and might be governed.