The article aims to examine, in light of the codification work of the International Law Commission and of the most recent practice, some issues concerning the allocation of responsibility between an organisation and its troop-contributing states for the conduct taken in the course of a multinational operation (with a specific focus on UN operations). After explaining the general rule of attribution of conduct based on the status of the multinational force as an organ or an agent of the organisation, this article will examine the validity of special rules of attribution of conduct based on the notions of 'effective control' or 'ultimate control' over the acts of the multinational force. Finally, I will discuss the possibility of dual responsibility of both the organisation and the troop-contributing state concerned. Keywords: responsibility for internationally wrongful acts, multinational operations, United Nations, Draft Articles on the Responsibility of International Organisations, peacekeeping operations.