The previous studies on stable isotopes of condensation water are all about fog, without any study about dew or water vapor adsorbed by soil. In most of the studies, more isotopes have been found in fog than in rainfall, due to differences in the temperature of condensation of the water vapor, as well as the history of the air mass producing the precipitation. Fog isotope values have a large range depending on the temperatures and vapor sources in the study areas. Advective oceanic fog is quite isotopically enriched compared to rain in the same area because it is an early-stage condensate representing a single-stage evaporation (over the open ocean)-condensation (at the coast) cycle. In tropical cloud forest where orographic fog and rain are from the same cloud and occur simultaneously, fog has been found to be more isotopically enriched than rain, but differences between fog and rain are relatively small. Inland radiation fog, with water vapor partially originating from terrestrially recycled water, has the larger deuterium excess value and δD and δ¹⁸O values than precipitation originating from water vapor evaporated from the oceans. Stable isotope techniques have been used in a few cases to evaluate possible contribution of fog water to stream flow, plant transpiration, or groundwater recharge. But few studies assessed quantitatively the contribution employing end-member mixing model. Directions for future research may include the stable isotope studies of dew and water vapor absorbed by soil in arid regions, the combination of D and ¹⁸O with other isotopes or chemical indexes to evaluate eco-hydrological roles of fog, the long-term and intensive sampling strategies in stable isotope studies of condensation water, and the design of fog collectors for stable isotope samples.