The potential of using stable isotopes of water was recognized in the 1930s, but not fully explored until the 1950s. Improvements in measurement techniques have facilitated use of isotopes in many contexts, and isotope hydrology has become mainstream. Reprinted papers and accompanying commentaries are presented. Topics covered are: A. Fundamentals, B. Atmospheric Water Cycle, C. Palaeoclimates, D. River and Lake Hydrology, and E. Groundwater.