The National Science Foundation's Hydrologic Sciences (HS) program is seeking grant proposals for fundamental research on continental water processes at all scales. The program supports observational, experimental, theoretical, and modeling approaches related to hydrologic processes, water fluxes, hydrologic transport, and the coupling of hydrological processes with other systems. The program is particularly interested in research that advances understanding of hydrologic responses to changes in land use, climate, or watershed management. Proposals will be evaluated based on their intellectual merit and potential broader impacts. The application deadline is not specified. Funding for successful proposals is not quantified, but the Geosciences program, under which the HS program is assigned, has recently awarded grants ranging from $79,139 to $4,893,936 with typical project periods of 1-5 years. The work is predominantly performed at academic facilities, field sites, scientific observatories, and research vessels across the United States, with opportunities for interdisciplinary and international collaboration.