Walter Langbein (1907--1982) contributed to the growth of scientific hydrology in a number of ways. His research publications introduced original concepts of both theoretical interest and practical importance. He served on a number of committees of the American Geophysical Union and played a key role in promoting new approaches in hydrological thinking. He played a major role in the launching of the International Hydrological Decade of 1965--1974 and in the establishment of the International Association of Hydrological Sciences Committee on Mathematical Models in Hydrology in 1967. He was a source of inspiration to many young hydrologists who have since made their own important individual contributions to that discipline. It is timely and useful to look back at his personal contribution to hydrology and to draw lessons on it for our future work. ¿ American Geophysical Union 1996