The weather on planet Earth is a vital and sometimes fatal force in human affairs. Efforts to control or reduce the harmful impacts of weather go back far in time. Inthis, the latest National Academies’ assessment of weather modification, the committeewas asked to assess the ability of current and proposed weather modificationcapabilities to provide beneficial impacts on water resource management andweather hazard mitigation. It examines new technologies, reviews advances innumerical modeling on the cloud and mesoscale, and considers how improvementsin computer capabilities might be applied to weather modification. Critical Issues in Weather Modification Research examines the status of the science underlying weathermodification in the United States. It calls for a coordinated national research programto answer fundamental questions about basic atmospheric processes and toaddress other issues that are impeding progress in weather modification.