Stable isotope ratios of hydrogen and oxygen in water are powerful tools for understanding the earth system, yielding unique insights into the dynamics of past, present, and possible future climate on timescales from sub-daily to orbital. Studies employing water isotopes have provided records of past and present climate change, tracers of hydrologic sources and sinks, and indicators of physical and ecological processes in the atmosphere and biosphere. Recently, innovative techniques allowing for water isotope measurements at high temporal frequencies and large spatial scales, new capabilities in simple and complex modeling frameworks, and advances in theoretical descriptions of isotopic processes have enabled a wide array of new research questions to be addressed. This session welcomes any work that focuses on the measurement, modeling, or application of water isotopes to better understand climate dynamics, hydrology, or ecohydrology.