The entities recognized as subjects of international law are, at present, only States and International Organizations. This approach leads the doctrine to consider everything else as "subject of international law". However, this restrictive perspective does not make it possible to grasp the changes in contemporary international law and the increasingly confirmed presence of non-State entities such as Non-Governmental Organisations (NGOs). Despite this presence of NGOs in the international sphere, in international conferences and before international courts, their legal status in international law has remained uncertain for more than a century. This study makes it possible to analyse the evolution of their role in various international systems while revisiting the questions of the legal personality and international legitimacy of NGOs. These entities are today in the midst of internal and external transformations that could enable them to achieve a new status in international law.