a b s t r a c tThe Gulf Cooperation Council (GCC) countries are situated in one of the most arid regions in the world, with extremely poor endowment of freshwater resources. Despite the water scarcity, the GCC countries have done well in providing water for their ever-increasing population and rapidly expanding economic base. However, this has been achieved only by resorting to relatively very expensive and costly investments in water supply sources and infrastructures manifested by desalination, water treatment, dam constructions, as well as groundwater overdrafting. Being an important vector for socioeconomic development, there is a need for the establishment of an efficient and sustainable water management system to ensure that the water sector can continue to serve the countries' development needs. However, currently the GCC countries are facing several major challenges that are threatening the water sector sustainability. These include increasing water scarcity, increasing costs for infrastructure and service delivery, resources deterioration, increasing environmental and economic externalities, and many others. The main driving forces of these challenges are population growth and changing consumption patterns, low supply efficiencies, lower rates of water reuse and recycling, and low energy efficiency in the water sector. The intensity of these challenges is expected to increase in the future due to the additional driving force of the impacts of climate change. Realizing these challenges, the GCC Supreme Council has issued in its 31st summit (2010) the directive of "serious and speedy steps should be taken and endorsed by the GCC Supreme Council toward a long-term comprehensive Gulf water strategy". In 2016, a GCC Unified Water Strategy, 2016-2035 (GCC UWS) has been finalized by the GCC Secretariat General and approved by the GCC Supreme Council. This paper presents the main challenges facing the sustainability of the water sector in the GCC countries, the formulated GCC UWS (main themes and strategic objectives and their policies, key performance indicators and targets), the potential financial, economic, and environmental benefits from its implementation, and its expected overall contribution to the water sector sustainability in the GCC countries.