The Hydrologic Sciences Program supports fundamental research about water on and beneath the Earth's surface, as well as relationships of water with material and living components of the environment. The program focuses on hydrologic processes, fluxes of water, and hydrologic transport. Observational, experimental, theoretical, and modeling approaches are supported. • The program supports research with a primary focus on continental water processes at all scales. • A major focus is the study of hydrologic processes, such as rainfall and runoff, infiltration and subsurface flow, and evaporation and transpiration. • Many projects involve the study of hydrologic transport, coupling of hydrological processes with other systems, or hydrologic responses to change. • The program supports research that involves observational, experimental, theoretical, and modeling approaches.