The period leading up to the fiftieth anniversary of the Declaration on the Principles of International Law concerning Friendly Relations and Co-operation among States was characterised by numerous claims of intervention by one State levelled against another State or group of States. The case of alleged Russian involvement in the presidential elections of the United States, the decision by some States to recognise a rival government in Venezuela, the provision of arms to fighting groups in Saudi Arabia in the conflict in the Yemen are but some recent examples. These claims raise the question of the scope, content and status of the duty of non-intervention in matters within the domestic jurisdiction of any State.