It is a commonplace to state that there is no universally accepted definition of international organizations (IOs). Until recently, the International Law Commission (ILC) used to identify IOs simply as "intergovernmental organizations." However, in its new project - drafting the rules on international responsibility of international organizations - ILC has provided a longer and more precise definition of IOs. For the purpose of the Draft Articles on Responsibility of International Organizations (DARIO), an entity will be considered as an IO if (1) it is established by a treaty or other instrument governed by international law, (2) it is possessing its own international legal personality; and (3) its members, in addition to States, are other entities (Art. 2(a)). This article analysizes this definition in order to assess its conformity with the practice and doctrine of international law. Moreover, this article tries to determine whether the ILC's definition is appropriate for the purpose of formulating the rules on international responsibility of international organizations. Firstly, the article concludes that the definition of IOs from Art. 2(a) of DARIO is both broad and narrow. Its first and second elements, i.e. the source establishing an IO and IO's possession of international legal personality, make the ILC definition broad. Obviously, the intention of the ILC was to include as many international entities which possess characteristics of IOs within the scope of its rules of responsibility. On the other hand, the definition is narrow since its third element - the requirement that its membership must include States - excludes from the scope of the DARIO those organizations which only have other international organizations as members. Secondly, the article points out that one element of ILC's definition, possession of own international legal personality, is at odds with the practice and doctrine of international law. Namely, the practice and doctrine clearly show that the legal personality of international organizations is above all contextual. However, the position of the ILC implies that all international organizations by the very fact of their existence possess international legal personality. This is due to ILC's attempt to put all international organizations into UN's shoes. Moreover, this implies that international legal personality of all IOs must be considered as "objective" - meaning that it does not require recognition of non-member states. This is also at odds with practice and doctrine of international law. Those accepting the idea of contextual legal person hood of IOs, advocate against the ILC's attempt to provide general rules of responsibility for IOs grounded on their person hood. However, this issue can also be viewed from another angle. Not only an IO can be responsible for violation only of those international obligation that it actually has, but the existence and scope of its legal personality should be assessed on the basis of its existing rights and duties. Therefore, the article concludes that, despite above mentioned shortcomings, the definition of IO given by the ILC seems to be an appropriate one for the application of the rules on responsibility of IO.