Major sources of groundwater recharge include rainfall, snowmelt, and infiltration from surface water features. The rate and generic behavior of recharge lie at the interface of understanding between hillslope, vadose zone, groundwater, and ecohydrology. Catchment hydrologists may view "subsurface runoff" as a simple loss term, while groundwater modelers may approximate "recharge" merely as a fraction of rainfall. As groundwater recharge is one of the main drivers of the hydrological system, appropriate quantification is required for robust model predictions. Accurate measurement of recharge is merely impossible, however, which makes it difficult to assess the accuracy of recharge estimates and, as a resultant, the accuracy of model predictions. The objective of this special issue of HESS is to collect the most recent scientific work on groundwater recharge. Relevant issues include the following:

– major processes influencing recharge, such as climate, soil, vegetation, plant– oil interactions, snowmelt, and land-scape features;
– new and improved methods to measure recharge directly;
– recharge signature in measured head fluctuations, isotope data, contaminants and nutrients, and other field measurements;
– improved interpretation of surface measurements to constrain recharge estimates;
– the role of the unsaturated zone: heterogeneity, preferential flow paths, root water uptake;
– conceptual modeling of the recharge process including alternatives to Richards' equation;
– different sources of recharge: rain, snow, leaking pipes and canals, ephemeral streams, etc.;
– water planning considerations of recharge;
– sustainable yield.