This contribution briefly discusses the methodological and conceptual issues faced by the ILC during its work on the responsibility of international organizations. It examines some of the key challenges faced by the ILC, including the lack of relevant international practice, and the diversity of international organizations. It argues that while the responsibility of international organizations remains an important topic for international law, the law is not yet developed enough for codification of secondary rules to apply to all international organizations. In some cases, this led the ILC to rely heavily on its Articles of States Responsibility. This approach pushed the work of the ILC closer to ‘progressive development’ of the law than to codification.