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Hydrological tracers rank among the most important tools in hydrology and hydrogeology. They improve our conceptual understanding of hydrological systems and support quantitative insights into water budgets, flow paths, groundwater recharge, groundwater-surface water interactions, hydrochemistry, geochemistry, ecohydrology and geomicrobiology. Recent advances in analytical techniques (e.g., high- frequency analyses of dissolved (noble)gases, stable water isotopes or microbial community compositions directly in the field, ultra low-level counting of rare noble gas radionuclides, or high-throughput sequencing of environmental DNA) now allow precise measurement of an unprecedented range of hydrologically important physical, chemical, and biological processes at spatial and temporal resolutions unthinkable just a few years ago. Moreover, owing to the recent surge in computational power and integrated models, we are finally enable to explicitly simulate the (reactive) transport of hydrological tracers throughout the entire hydrosphere. This session aims to showcase recent advances, innovations, and emerging methods in measuring, simulating, and interpreting hydrological tracers. In particular, it seeks to highlight multidisciplinary approaches that provide an improved conceptual and/or quantitative understanding of complex hydrological, hydrogeological and ecohydrological systems. Because acquisition of hydrological tracers also supports the decision-making process, the goal of this session also lies in demonstrating studies which helped improving water resources management and making the exploitation of our precious water resources more sustainable and adaptable to future anthropogenic and climatic perturbations.