Although international law applicable to transboundary aquifers is still in an early stage of development, ground water resources on nation’s frontiers are now garnering growing international attention. This article examines the chief formal and informal mechanisms that have been proposed or implemented for the assessment, use, allocation, and protection of transboundary aquifers and identifies the legal trends and priorities emerging from these instruments. It also considers gaps and shortcomings in the emerging administrative regime and offers recommendations for the further development of the law.