The principle of distinction in International Humanitarian Law sets up two entities, the civilian and the combatant, and organises the relationship between them. This socio-legal chapter draws on original research from South Sudan to explore how this principle is operationalised in humanitarian–peacekeeper interactions. Humanitarian actors routinely invoke ‘distinction’ as they navigate operational dilemmas with respect to the use of military assets, and in their relationship with the UN Mission in South Sudan more generally. Two ‘ideal types’ of humanitarian actor emerge here. The first type takes a strict approach to distinction, thinking long term and eschewing military asset use that undermines distinction. The second type interprets distinction flexibly and balances it with other goals such as reaching people in need; this exposes a hidden conflict between the principles of distinction and humanity. Through these everyday interactions – which sometimes involve drawing lines within the civilian category – humanitarian actors produce distinction in law, in practice, and in perception.