The field "hydrogeophysics" emerged in the 1990s as a multi-disciplinary subject that focuses on the use of geophysical methods for characterising subsurface features, determining hydrogeological properties and monitoring processes relevant to soil and groundwater processes. Hydrogeophysical methods can allow large scale aquifer characterization, previously unobtainable through conventional hydrogeological techniques. In addition, time-lapse deployment of appropriate methods can give useful insight into complex subsurface processes, aiding hydrological model development and the assessment of groundwater restoration strategies. Here, we review hydrogeophysical approaches and highlight potential new (or emerging) application areas, such as hyporheic zone characterization and monitoring soil-water-plant interactions. We discuss new approaches for analysis of hydrogeophysical data, including the fusion of multi-modality data and hydrological models. We emphasise the need for appropriate constitutive relationships, which are fundamental to most hydrogeophysical investigations. Finally, we list a number of key challenges, namely resolution and scale of method, computational demands on multi-dimensional modelling and the need for quantification of the information content in the various hydrogeophysical data sources.