Ethiopia, the second most populous country in Sub-Sahara Africa, is suffering from chronic drought, rapid population growth and land degradation. The famine in Ethiopia was mainly associated with erroneous rainfall distribution on some parts of the country including Raya Valley. A large proportion of these draught-affected areas were found in Tigray Regional State. Raya Valley is found in the Northern part of Ethiopia. The annual amount of rain fall is relatively small and erratic as compared to other parts of the country. This makes ground water to be a better option for a water supply for both agriculture and drinking. This book characterises the groundwater from hydrological, geological and chemical perspective inorder to give a clear picture for groundwater developer, planner and managers in the region and in the country in general.