<p>Forested catchments are ‘hydrological hotspots’ in the world as they act as major sources of high-quality water on Earth and provide essential ecosystem services. Understanding their hydrological functioning is therefore critical for effective land, water and forest management. While field and modelling studies have often focused on individual catchments or multisite intercomparisons, a global analysis of runoff processes in forested catchments is currently lacking, limiting our understanding of how biotic and abiotic factors interact to control these processes across the world. Here data are synthesized from 691 globally distributed forested catchments to identify the main controls on runoff processes, streamflow response and streamflow prediction and assess how these controls vary with climate. Using this global dataset, seven classic hypotheses and an original one are tested. The results corroborate some theories while challenging others, offering new, process-based insights into the intertwined factors controlling runoff generation in forested catchments worldwide.</p>