For the analogy between States and international organizations to be plausible, two conditions must be satisfied. First, international law has to admit of international organizations as a general category of entities to which a common set of rights, obligations and capacities can apply, as is the case with States. This requires seeing them as international legal subjects proper - as opposed to mere treaty transactions between their member States - and identifying the unifying principle that brings a wide range of existing institutions within the same category. Second, there must be attributes which all the entities falling under that general category share which can be persuasively compared with attributes shared by the category formed by States. In discussing these theoretical assumptions in light of relevant practice and precedent, the chapter revisits debates that have taken place within the International Law Commission with respect to the definition, legal personality and capacities of international organizations, as those provide an illustration of the evolution in thinking on the status of international organization under international law. The aim is to offer a fresh perspective on the elusive position that these institutions occupy in the international legal system.