Cloud seeding is a type of weather modification that aims to change the amount or type of precipitation, mitigate hail or disperse fog. The usual objective is to increase rain or snow, either for its own sake or to prevent precipitation from occurring in days afterward.

Weather modification is the act of intentionally manipulating or altering the weather. The most common form of weather modification is cloud seeding, which increases rainfall or snowfall, usually for the purpose of increasing the local water supply. Weather modification can also have the goal of preventing damaging weather, such as hail or hurricanes, from occurring; or of provoking damaging weather against an enemy, as a tactic of military or economic warfare like Operation Popeye, where clouds were seeded to prolong the monsoon in Vietnam. Weather modification in warfare has been banned by the United Nations under the Environmental Modification Convention.