ABSTRACTResearch on glacier mass balance began in the U.S.A. about 50 years ago. More complete studies of climate, snow and ice balance, and the hydrology of glaciers were initiated for the IGY in 1957 and the IHD in 1966. Investigations included the magnitude and geographic distribution of normal mass balance processes and unusual phenomena such as out-bursting, accumulation of ice by freezing of water in firn, and ablation of glacier ice by volcanic activity and by calving. Glacier size has been found not to be a simple function of climate as is widely imagined. Glaciers can increase with a warming of climate and can shrink due to calving instability mechanisms. Numerical modeling of glacier balance and runoff have appeared in the past decade only. Glacier research has also produced a new understanding of the nation's climate, water resources, and flood hazards because glaciers exist in very moist rather than very cold climates and produce very high runoff rates.