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The accumulation of snow during winter and its subsequent melting during warmer months provide most of the water needed for the human populations located along the semiarid western and eastern slopes of the Andes in central Chile and central-western Argentina. The societies in these regions can be characterized as ‘hydraulic societies,’ as social tissues are strongly associated with intensive use of water resources that historically have been adapted to ‘control’ a hostile natural environment. This chapter first discusses various empirical analyses of snowpack and streamflow records that demonstrate (1) the dominant influence of snowmelt on the hydrologic regimes of the main rivers of the region, (2) the impressive similarities in these records at interannual and interdecadal timescales, and (3) the strong relationships that exist with El Nino–Southern Oscillation (ENSO) features in the tropical Pacific. The authors also use the snowpack and streamflow records available to identify the most severe dry and wet periods in this portion of the Andes over the past 100 years. Two recently developed snowpack reconstructions that extend the instrumental records for several centuries are subsequently discussed in an attempt to provide evidence that may help assess the recent patterns observed in the instrumental records in a long-term perspective. This evidence may also be used to test the time stability of the relationships with large-scale ocean–atmosphere features and to validate the results from global and local modeling exercises intended to project future hydroclimatic changes in this region. The final discussion is on the inherent vulnerabilities associated with the scarce water resources of the inhabitants of the Rio Mendoza Basin in Argentina. This exercise allows an interesting analysis to better understand the historic, current, and possibly future socioeconomic situation of the different players of this hydraulic society. Comprehensive assessments integrating results from natural and social studies are suggested as an innovative approach to anticipate future vulnerabilities to water shortages and to develop adaptation strategies toward resilience.