This article suggests that the variety and complexity of international partnership programmes, especially those that contract major fund flows, can be sustained only if partners are able to allocate roles and responsibilities amongst themselves. The premise of this article is simple. Lest there be any doubt, agreed terms set forth in signed agreements and adopted partnership documents should be considered ‘rules of the organization’ under the ario, and should be recognized in allocating responsibility among international organizations and other partners in international development initiatives. A practical look at trust-funded partnership programmes involving the World Bank underscores the importance of lex specialis under the Articles on the Responsibility of International Organizations, including with respect to claims by third parties. At stake is the viability of such collaborative international development initiatives, which rests on the ability of partners to legitimately set their own terms for acknowledgment by others.