The history of forest hydrology studies in the UK is reviewed in the context of the competing uses of the upland areas of the country for water supply and for timber production. This paper demonstrates the importance of conducting process studies to explain, and if necessary extrapolate, the hydrological differences due to land use that are observed on the catchment scale. Forest is compared with other shorter vegetation types, and the impact of forestry activities (such as drainage and felling) on evaporation and streamflow is also discussed.