In the past few years there has been considerable research on the modeling of rainfall and runoff in space and time. At the same time, there have been a number of technical innovations which have the potential to greatly facilitate modeling. These include hardware and software developments in radar estimation of rainfall, digital topography, geographic information systems, remote sensing, and flow and water-level instrumentation. It is apparent, however, that very little of this new capability is currently utilized in hydrologic design. This special session, sponsored by the Precipitation Committee of the Hydrology Section at the 1989 Fall AGU meeting, explored various facets of this issue. Participants included representatives of county, state and federal agencies, engineering consultants, and university researchers.