This chapter critically reviews our knowledge of hydrological processes in the chief zonal forest types within the Lesser Himalaya, notably the Shorea-dominated forests of the tropical lowland and foothills, the subtropical pine and Castanopsis-dominated forests at intermediate elevations, and the temperate oak- or conifer-dominated forests above ~2000 m. Processes at the hillslope and headwater catchment scale are compared between forest types. Next, the soil and water impacts of various forest uses and interventions are addressed, along with those of forest regrowth after agricultural abandonment and (pine) reforestation. Overall, quantitative knowledge of forest hydrological processes in the region is limited, particularly on forest water uptake and runoff generation. The chapter offers various recommendations for further research, notably on changes in vegetation water use during forest succession, the hydrology of cloud-affected forests with potentially high water yields, and the water dynamics of agroforestry systems. To document impacts of climate change on forest hydrological processes, it is recommended to establish ‘critical zone observatories’ (CZOs) in which the stocks and flows of water are monitored. Maximum synergy may be achieved by locating such CZOs at sites with past or ongoing research that together capture the chief geological and climatic variations along the mountain chain.