 The basis for catchment classification, transferability of information, generalization of hydrologic understanding, and potential impacts of environmental change is derived from hydrologic similarity between catchments, which is based on their response to precipitation input. A Bayesian clustering scheme is used to separate 280 catchments in the Eastern U.S. into 9 homogeneous classes based on their signatures, to find as hydrologic response characteristics that provide insight into the hydrologic function of catchments. The analysis reveals several hypotheses regarding controls on individual signatures. This article is offered by K. Sowitz, T. Wagoner, M. Savapolin, and others.