The spatial and temporal variation in the stable isotopic composition of precipitation collected at 13 monitoring stations across Russia between 1996 and 2000 was determined. The results show that eastward moisture transport over the continent generates a tendency toward more negative isotopic content farther inland throughout the year. This negative isotopic gradient can be explained by the gradual rain-out of moist, oceanic air masses, which are transported inland by westerly winds. In summer, however, the isotopic gradient is less clear, because of additional moisture that is supplied from land surfaces. The isotopic pattern of summer precipitation is less sensitive to moisture content but is largely influenced by the original moisture. In Siberia, more than half of the moisture that forms summer precipitation originates from land surfaces; thus the isotopic content of precipitation in this region is controlled mainly by the contribution of recycled water; e.g., the proportion of water that is recycled (recycling ratio) and its isotopic composition. Comparisons of the observed summer isotopic content of precipitation and the calculated recycling ratio from National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data show that about 20% of the total variability of isotopic content during summer can be linked to the recycling ratio. About 45% of the summer isotopic variability cannot be explained by either temperature, which is used as an indicator of moisture content, or the recycling ratio. This remaining variability may be linked to the isotopic variability of the recycled water that falls as observed precipitation. It may be that the isotopic content of recycled water varies in space and time and the isotopic distribution in summer precipitation reveals details in this feature; thus it might be possible to deduce information about the interaction between land and atmosphere in the hydrologic cycle from the isotopic content of precipitation.