Robert E. Horton is best known as the originator of the infiltration excess overland flow concept for storm hydrograph analysis and prediction, which, in conjunction with the unit hydrograph concept, provided the foundation for engineering hydrology for several decades. Although these concepts, at least in their simplest form, have been largely superseded, a study of Horton's archived scientific papers reveals that his perceptual model of infiltration processes and appreciation of scale problems in modelling were far more sophisticated and complete than normally presented in hydrological texts. His understanding of surface controls on infiltration remain relevant today.