A central concept found in the 1907 Hague Regulations Respecting the Laws and Customs of War on Land is the notion of ‘belligerents’. The formal status of ‘belligerents’ or, in more modern terms, ‘combatants’, is limited to international armed conflicts. One of the crucial functions that the status fulfils relates to distinguishing those who are legitimate objects of attack from those who enjoy protection. Combatants are legitimate targets, while civilians are not, unless and for such time as they directly participate in hostilities. Civilians are defined as all those who are not combatants. Because the formal status of ‘combatant’ is limited to international armed conflicts, the principle of distinction cannot be conceptualized in the same way in non-international armed conflicts. Who, then, may be targeted in non-international armed conflicts and under what conditions and who is conversely immune from being made the object of attack and enjoys protection against the dangers arising from military operations by virtue of the status of ‘civilian’? This article argues that, in principle, members of armed forces of both state and non-state parties to a non-international armed conflict are legitimate targets and all those who are not such members are to be considered civilians. However, the practical operationalisation of the principle of distinction in this way faces a number of difficulties. Due to the variety and changing nature of organised armed groups, a more differentiated approach is required in striking a reasonable balance between military considerations and humanitarian concerns.