The domestic allocation of responsibility for the treaty-making is a significant question of the constitutional separation of powers, determining whose voice is accounted for in the state’s conduct of its foreign relations. Certain States, including South Africa, have sought to augment democratic participation in the exercise of their foreign relations by giving a role for the legislature and even the judiciary in the State’s treaty-making power. The South African developments will be set out and compared with examples from different jurisdictions, drawing out global constitutional developments in re-allocating aspects of treaty-making authority away from the executive. It considers how international law takes account of these constitutional developments, if at all. It concludes by considering possibilities for change in this area, particularly to augment protection for domestic separation of powers and democratic participation in treaty making in South Africa and beyond.