The Gulf Cooperation Council (GCC) countries, which consist of Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and United Arab Emirates, possess abundant oil resources but scarce water resources. Low rainfall and high evaporation rates threaten sustainable development in this region. Currently, water demands for domestic and industrial sectors in these countries are mostly met by non-conventional resources such as desalinated water and treated wastewater. In order to augment the freshwater resources, better water management planning, with suitable assessment tools, is necessary. The use of stable and radioactive environmental isotopes has proven to be a powerful assessment tool in many hydrological problems. Combination of previous isotopic and hydrological studies of the Arabian Peninsula could provide an insight on the dynamics of natural processes affecting this water-scarce region. This paper groups many of these studies into various categories based on their objectives, including identification of recharge areas, assessment of groundwater dynamics, and estimation of groundwater age and residence time. Results of previous isotope studies in the GCC countries are put together to identify the sources of precipitation and estimate rates of evaporation, which is the major cause of water loss in these countries. Mediterranean Sea is the major source of vapor for all GCC countries. Local moisture in the UAE is derived from the Arabian Sea and the Indian Ocean, whereas in Saudi Arabia it either originates from the Atlantic Ocean, the Arabian Sea, or the Indian Ocean. Evaporation alters the isotopic composition of groundwater which is mainly controlled by relative humidity that varies between 20% and 90% in the GCC countries. The slope of the evaporation line, compared to Local Meteoric Water Lines (LMWLs), for Bahrain, Kuwait and northern Oman indicates a moderate rate of evaporation due to rapid infiltration of storm water. In contrast, the evaporation line slope for Qatar, southern Oman and Saudi Arabia are higher than the slopes of the LMWLs showing a relatively low rate of evaporation. The UAE groundwater slope is smaller than that of LMWL indicating high evaporation rate of surface water prior to infiltration. The age of groundwater in the GCC countries indicates residence time since late Pleistocene and early Holocene. Hydrochemical data show that groundwater in the GCC countries is contaminated due to evaporation, irrigation return flow and saltwater intrusion. © 2021 Elsevier B.V.