The chapter delves on the multi-centennial experience of Portugal and Spain in managing and developing the water resources of their shared hydrographic basins; apprehends the factors leading the two Iberian states to revise their legal regime; analyses the contents and significance of the newest Convention adopted in 1998 as well as the record of its implementation. It concludes by drawing a very positive balance of the latter and looks prospectively at the possibilities to further enhance the regime and optimise its application.