Humanitarian aid has been a malleable concept. It covers a broad range of activities including emergency relief delivered to people struck by disasters; longer term efforts to prevent suffering from famine, ill-health or poverty; or humanitarian intervention. The boundaries of humanitarianism have often been blurred. Existing narratives for the twentieth century provide no satisfactory explanation for the evolution of the field. We need to highlight instead historical conjunctures and contingencies such as wars and post-war periods, empires and decolonization. The emphasis on conflicting forces and multi-layered structures at particular moments in time provides a historical perspective revealing fundamental dilemmas faced by international humanitarian aid to the present day.