Traditional approaches to hydrology have favoured a reductionist perspective. This text argues that hydrologists of the 21st century must increasingly look beyond the traditional boundaries of river channel or river catchment areas to consider new questions: firstly, how water resources should be managed in an integrated and sustainable way with a growing appreciation of the global dimension to water resource problems; secondly, how the search for solutions to water pollution, flooding, drought and environmental degradation requires a broader understanding of transboundary connections between components of the hydrosphere across a range of spatial and temporal scales. In an emerging age of water shortage, increasing dependence will also be placed upon existing monitoring and water distribution networks. Advances in data gathering systems and hydrological modelling have created new opportunities for assessing and managing these water resources. Similarly ecohydrology and palaeohydrological techniques are generating new types of data for model development and testing. This text will provide an excellent overview for post-graduates and researchers studying hydrology, meterology, environmental science and related topics. It will also be useful as supplementary reading for 2nd/3rd year undergraduates in these areas. The ruins of the flooded Derwent village emerged from Ladybower Reservoir, Derbyshire UK in autumn 1995. This image highlights a number of issues pertinent to contemporary hydrology such as: winter droughts severely restrict the replenishment on upland communities; the uneasy relationship between forestry and water resources in water supply catchments; water quality problemsassociated with acidification, turbidity and sedimentation; the aesthetic and ammenity value of impounded waters