The Hydrologic Sciences (HS) program, administered by the National Science Foundation (NSF), is seeking grant applications to support fundamental research on the fluxes of water in the environment and the water cycle. The program focuses on processes from rainfall to runoff, evaporation and transpiration, soil and aquifer flow, and the transport of water-borne components. Key objectives include linking water fluxes across terrestrial system boundaries, understanding how the water cycle is altered by land use and climate, and exploring physical, chemical, and biological processes coupled to water transport. The program will consider proposals involving expertise from basic sciences, engineering, and mathematics, and may require joint review with related programs. Synthesis projects are also of interest. Funding for this grant opportunity is provided through the NSF's Geosciences program (CFDA 47.050), which supports fundamental research and educational initiatives across various Earth science disciplines. The Federal Grant Awards under this program have demonstrated substantial diversity, with recent awards ranging from $79,139 to $4,893,936 and typically spanning 1-5 year project periods. The work is predominantly performed at academic facilities, field sites, scientific observatories, and research vessels across the United States, with numerous opportunities for interdisciplinary and international collaboration.