It may seem anachronistic that different rules apply to international armed conflicts (IAC) and non-international armed conflicts (NIAC), and that the legal character of an armed conflict can have significant consequences for combatants, civilians and victims of alleged war crimes. The Intertional Committee of the Red Cross, in the lead up to the 1949 Diplomatic Conference, had proposed that the Conventions should apply to any situation of armed conflict regardless of its legal character but that proposal was rejected by states. Irrespective of the desirability of a simplification in approach, the current state of the law of armed conflict (LOAC) maintains the distinction between the two categories of armed conflict. Section 1 of this chapter briefly outlines the significance of the distinction between IAC and NIAC. Section 2 outlines the treaty provisions relevant to the characterisation of conflicts and identifies the lack of a treaty definition of an armed conflict. Section 3 examines the question of how to characterise armed conflicts, and proposes two key principles: (1) that the legal character of an armed conflict is determined by the nature of the parties to it; and (2) that the only armed conflict which is international is one between two or more opposing states.