The discipline of International Relations owes its origins to the study of war and peace. But are today’s wars so different from their predecessors that we need a new mindset? To answer that question, this chapter begins with warfare’s diverse ends and means before considering five leading issues: the role of violence in warfare; the extent to which that violence is organised; the political nature of war; the interactive nature of warfare; and the scope and scale of war. The argument presented here is that war’s essential features have not changed as much as we might think. This should make us sceptical about claims that the role of war in international relations has somehow been revolutionised.