While groundwater occurs under all the lands of the world, it does not follow political boundaries and is infl uenced by human action of pumping from wells. It may be the only water source in many locations. Groundwater overuse and misuse threatens the resource for water supply around the world. Even though it is an essential substance of life, over 1 billion people out of the current 6 billion world inhabitants lack adequate water supply (UNESCO, 2003). “Some 47% of the land and 40% of the population of the world live in transboundary river basins and therefore competition over the water resources in these basins is expected to be intensifi ed over the coming years” (Tsakris, 2003). Since the earth can only support the food requirements of 500 million people without management (UNESCO, 2003), irrigation, the largest water use worldwide, will continue as a necessary practice. Furthermore, wastewater as well as other wastes, if improperly disposed, can reduce the amount of safe water available for use. In these contexts, we will examine groundwater use and its transboundary and international implications. Clearly, national claims on the use of groundwater have economic consequences for this subsurface resource shared by neighboring countries. Confl icting claims indicate the value of groundwater in these situations. Climate change may focus greater attention on transboundary concerns related to groundwater.