The attempt to establish a New International Economic Order (NIEO) during the 1970s was an acrimonious period in international diplomacy and quite clearly failed, in retrospect, to achieve anything like the substantive change envisaged. This article considers one non-governmental attempt to move the debate forward, the 1986 International Law Association (ILA) Declaration on Progressive Development of Principles of Public International Law relating to a New International Economic Order. The article revisits the 1986 Seoul Declaration and considers to what extent its principles of international law remain valid for an economic system that has changed dramatically over the last twenty years. The article concludes that not only is the Seoul Declaration remarkably apposite to the current situation, but it has been re-energised by the emergence of the notion of sustainable development, itself a major topic within the International Law Association. In that sense, the Seoul principles – as now supplemented by the 2002 ILA New Delhi Declaration of Principles of International Law relating to Sustainable Development – remain foundational not only to the functioning of an equitable economic system but also, in the light of changing expectations, a sustainable international community, more generally.