In general, improvements in real-time hydrologic modeling and forecasting will depend upon developments related to numerical weather prediction models, watershed modeling, remote sensing methods, and methods for handling the space-time variability of rainfall at various scales. Foufoula-Georgiou and Krajewski [this issue] review advances related to rainfall modeling, estimation, and forecasting. Krzysztofowicz [this issue] reviews developments relating to flash flood forecasting, main-stem flood forecasting, and flood warning systems. Krzysztofowicz [this issue] documents the relatively recent developments in flood forecasting relating to the coupling of flood forecasting systems with flood warning decisions and emergency response plans. In some sense, these integrated flood forecasting/warning/response systems described by Krzysztofowicz [this issue] are good examples of an emerging class of decision support systems described by Watkins and McKinney [this issue]. As significantly more data become available with, for example, the implementation of the Next Generation Weather Radar (NEXRAD) system over the entire U.S., our understanding of the space-time variability of rainfall at various scales should improve.