In 2002, the UN International Law Commission added to its program of work the topic of Shared Natural Resources: transboundary groundwater, oil and gas. Six years later, the UN ILC completed its work on the first sub-topic by adopting at second reading nineteen draft articles on the law of transboundary aquifers. The draft articles were then deferred to the UN General Assembly, which adopted Resolution A/RES/63/124 including the draft articles in annex. In the Resolution, the UN GA “encourages the States concerned to make appropriate bilateral or regional arrangements for the proper management of their transboundary aquifers, taking into account the provisions of these draft articles”.The paper will go through the main principles codified in the draft articles. The UN ILC had benefited from a unique cooperation on the science of hydrogeology from UNESCO’s International Hydrological Program; hence it considered and covered issues of main importance for hydrogeologists.