Argentina, Brazil, Paraguay and Uruguay signed the Guarani Aquifer Agreement on 2 August 2010. This is the first international treaty regarding the management of a specific transboundary aquifer to have been adopted after the UN International Law Commission (UNILC) adopted the Draft Articles on the Law of Transboundary Aquifers, which have been annexed to UN General Assembly Resolution 63/124. The latter encourages States to take into account the Draft Articles when devising arrangements for the management of specific transboundary aquifers. The Guarani Aquifer Agreement, therefore, is a first response to this call from the international community. In this article the background to the Guarani Aquifer Agreement is explored, including an overview of the key characteristics of the Guarani Aquifer System and the steps that have led to the adoption of the Guarani Aquifer Agreement. Sovereignty, the obligation to cooperate and the incipient institutional framework are discussed as key elements arising from the Guarani Aquifer Agreement. Finally, the article argues that a link between the latter and the UNILC Draft Articles can be appreciated. This link has important practical implications especially in relation to the applicability of the UNILC Draft Articles for interpretation purposes of the Guarani Aquifer Agreement.